Thomisus onustus

Last updated

Thomisus onustus
Crab spider (Thomisus onustus) with prey nettle tree butterfly (Libythea celtis).jpg
with prey nettle tree butterfly (Libythea celtis) on spearmint (Mentha spicata), Pirin National Park, Bulgaria
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Araneae
Infraorder: Araneomorphae
Family: Thomisidae
Genus: Thomisus
T. onustus
Binomial name
Thomisus onustus
Walckenaer, 1805 [1]
Subspecies [2]

T. o. meridionalisStrand, 1907

Thomisus onustus is a crab spider belonging to the genus Thomisus . These spiders are found across Europe, North Africa, and parts of the Middle East and Asia. T. onustus reside in flowers in lowland vegetation, and females are distinguished by their larger size and ability to change color between white, yellow, and pink as a means of matching flower color. This cryptic mimicry allows them to both evade predators and enhance insect prey capture abilities. Males are smaller, more slender, and drab in coloration, usually green or brown. T. onustus is also distinguished by its distinct life cycle patterns in which spiderlings emerge in either late summer or early spring. Furthermore, T. onustus have developed a mutualistic relationship with host plants where spiders feed on and/or deter harmful florivores while benefiting from the plant’s supply of pollen and nectar, which T. onustus spiders are able to use as food sources, especially during periods of low insect prey abundance.



Purple camouflage. Thomisidae - Thomisus onustus.JPG
Purple camouflage.

T. onustus is a medium sized spider that exhibits sexual dimorphism, with females between lengths of 7-11mm and smaller males ranging between lengths of 2-4mm. (2,3). Females are heavy-bodies and mostly stationary, whereas males are slender and more motile. [3] [4] Females have a pink, yellow, or white prosoma and males are brown to green-yellow in color. Both sexes have a triangular opisthosoma. [4] This species can be distinguished from its close relative Thomisus zyuzini by its long ventral tibial apophysis and retrolateral tibial apophysis, the arrangement of the basal tibia tubercle on the male palp, and the circular intromittent orifice, which is oriented anteriad in the epigynum. [5]


T. onustus are members of the genus Thomisus, which includes around 150 described species, and is well supported as being monophyletic. It is relatively morphologically homogeneous genus, with synapomorphies that include circular scopula hairs (when viewed as a cross section), bulbuses that are subequal in length and width, disk shaped tegulums, sperm ducts that follow a circular peripheral course through the tegulum, and a lack of conductors and median apophyses. Subgroupings within Thomisus are not well supported, indicating a potentially paraphyletic genus. [6]

Habitat and distribution


T. onustus typically reside on shrubs and within lowland vegetation, preferring warmer areas. [7] They inhabit a wide variety of flowers and herbs, usually staying at the flowering peaks. [5]


T. onustus are distributed across Europe, North Africa, Turkey, Caucasus, Russia (from Europe to South Siberia), Israel, Central Asia, Iran, China, Korea, and Japan, preferring warm areas. [4]



While overall size is smaller, in terms of prey:predator length ratio, juvenile spiders capture larger prey than late instar and adult females. [3] Pollen feeding is particularly important for spiderlings, as it allows them to survive beyond what yolk reserves would otherwise allow. Due to the lack of amino acids, especially tyrosine, in pollen grains, spiderlings that feed exclusively on pollen are unable to molt versus spiderlings that feed on insect prey. [8]


Predatory feeding

T. onustus are summer-stenochronus spiders (summer reproductive season) and sit-and-wait predators. They stay in flower corollas and wait for insect prey including bees (Apoidea), butterflies (Lepidoptera), hoverflies (Syrphidae) [8] ,diptera, hymenoptera, and other spiders. T. onustus are cursorial spiders and do not use silk for prey capture. Instead, they use their long raptorial forelegs to ambush nearby insects. They frequently prey on insects far larger than themselves, ranging from 1.25 to 16.00mm in length. [3]   Males feed less and tend to prey on smaller insects. [7]

Non-predatory feeding

During periods of insect food shortages (ie. during inclement weather conditions), T. onustus are capable of using pollen and nectar as food sources for extended periods of time as a starvation survival strategy. Spiders will actively visit flowers of multiple species, such as those from Asteraceae and Asteroideae, for feeding. As Asteraceae species present pollen in an allotropic manner (pollen grains are exposed on the capitulum surface), spiders are able to acquire them easily. Since pollen grains are unable to pass through the cuticular platelets of spider pharynxes due to their relatively large size (> 1μm), pollen is consumed via extra-intestinal digestion, with nutrients likely extracted through apertures in pollen grains. [8]

Reproduction and life cycle

In the summer of their second year, toward the end of their lives, female spiders weave between two and four cocoons for egg laying. Spiderlings from the first egg sac emerge during late summer. This gives them access to more abundant prey resources, allowing them to obtain sufficient energy reserves to hibernate in vegetation outside of the cocoon during winter months. Spiderlings from egg sacs woven later, on the other hand, remain in the egg sacs through winter and emerge in early spring of the following year when prey is far scarcer, necessitating the use of pollen feeding to supplement nutritional and energy needs.

With two generations per year and the spring generation larger than the summer one, T. onustus females of both generations generally develop throughout the year whereas spring generation males grow faster, reaching maturity with second generation females from the prior year. Summer males, on the other hand, develop for a longer period, molting several times, and reach maturity in the summer of the next year with first generation females. Developmental rates for both sexes are highly variable, with spiders at different developmental stages found throughout the year. [8] Overall, the rate of development, duration of instars, number of molts, and molting times are all highly variable within the species. [7]

Brood size

The number of eggs laid varies widely for T. onustus, ranging from less than ten eggs to over 400 within each cocoon. Cocoons laid in early spring consist of far more spiderlings than those laid in the late summer. Unlike the more variable developmental stages of T. onustus, the period of cocoon, or the time between the laying of eggs and emergence of spiderlings, is generally around one month irregardless of season. This can be attributed to the insulation provided by the cocoon, making eggs less susceptible to seasonal and/or temperature changes. [7]


T. onustus typically molt at regular intervals up to the third and sixth instars provided they obtain adequate nutrition. [8] After eclosion from the cocoon, spiderling sex differences are not yet visible. By the second molt, the swelling of pedipalp tips distinguishes males. Males typically reach maturity after between three and five molts. Unlike males, females molt far more, reaching maturity after six to nine molts. As such, males typically mature after two and a half months and females after over a year. Due to shorter male life spans, sibling mating is, therefore, impossible. [7]

Life span

The maximum life expectancy of these spiders is 600 days, and female spiders have greater life expectancy than males (several months versus several weeks). [7]

Parental care

T. onustus usually attach egg sacs to leaves. Unlike some other cursorial species, females do not enclose themselves within the sac, instead continuing to catch prey during egg-guarding. [3]


T. onustus are primarily preyed upon by insectivorous birds. While their crypsis is imperfect, meaning that they do not perfectly match flower color, making them slightly detectable, T. onustus generally suffer little from bird predation. This is because it does not pay birds to specialize on crab spiders due to their uneven distributions and crypsis. T. onustus tend to prefer flowers with colors they can match (usually white or yellow), even when they could attain greater hunting success on other flowers. This is due to the increased predation risk of residing on flowers that would make them more conspicuous. [9]

Protective coloration and behavior

Thomisus onustus on Orchis purpurea Thomisus onustus on Orchis purpurea.jpg
Thomisus onustus on Orchis purpurea

T. onustus females are able to change their entire body color as a means of mimicking the color of flowers where they reside and capture prey. Possible colors include pink, shiny yellow, and white, sometimes with a bright medial stripe. Female color changes usually take several days in order to adjust to flower backgrounds. Males are usually yellow-green to brown in color and do not exhibit color changes. [10] Female aggressive mimicry provides camouflage from predators and works to fool insect prey, usually pollinators of flowers on which spiders reside. Spiders are capable of mimicking chromatic contrast of different flower species, allowing them to be cryptic in the color-vision systems of both avian predators and hymenopteran prey. More specifically, they are able to mimic flower color in four cone types corresponding to UV-blue-green-red for birds and three cone types, UV-blue-green, for insects. When aiming to detect smaller targets and/or see over larger distances, birds and bees preferentially use achromatic vision (brightness) over color contrast. As such, T. onustus mimicry also applies to achromatic vision as they are able to modulate both their achromatic and chromatic contrast [11]

Mutualism with plants

Female Thomisus onustus sharing its flower with velvet mites (cf. Eutrombidium rostratus). Spider and mites May 2008-1.jpg
Female Thomisus onustus sharing its flower with velvet mites (cf. Eutrombidium rostratus).

While T. onustus can deter certain pollinators, such as bees, that are more able to detect the spiders, T. onustus have had key impacts on floral trait evolution. Following florivore attack, plants are adapted to release floral volatile emissions that attract T. onustus, which consume and/or deter florivores. The compound β-ocimene, produced by plants in both floral and leaf tissues, acts as an attractive signal for both T. onustus and pollinators. This leads to overlapping floral preferences for both the spiders and their prey, providing a strong selective mechanism for sit-and-wait tactics of prey capture. Furthermore, β-ocimene is produced by 71% of plant families, explaining the broad range of flowers in which T. onustus might stay in. While T. onustus can harm plant fitness in the absence of florivores, they provide an overall benefit to plants threatened by florivores. As such, plants attract T. onustus only when florivores are present by inducing β-ocimene emission, making infested flowers more attractive to spiders. This mechanism generates strong selection on plants to develop a mutualistic relationship with T. onustus and suggests a key role for the spiders in the evolution of floral traits. [12]



Yellow coloration is likely due to the presence of ommochrome compounds and/or their precursors, such as xanthommatin and 3-hydroxykynurenine, deposited on hypodermal layers, which lie above specialized guanocyte cells full of guanine crystals, which lead to light scattering. Incident light is reflected from guanocytes back through pigment-containing hypodermal layers. White coloration is likely due to high concentrations of the transparent ommochrome precursor kynurenine and the reflection from guanine crystals. These explanations account for human-perceived white to yellow changes via differential pigment deposition in the hypodermis, but do not explain variations in UV reflectance.

Thomisus Onustus in Behbahan, Iran Thomisus Onustus in Behbahan, Iran.jpg
Thomisus Onustus in Behbahan, Iran

Color change abilities are due to contributions from both epithelial and cuticular layers, with epithelial cells modulating ‘human-visible’ changes. The cuticle of T. onustus is not equivalently transparent across the color spectrum, indicating a role in color variation. The cuticle limits the maximum reflectance that can be produced from the UV range and, as such, offers a barrier against potential UV photo-damage. Guanine crystals, present in the hypodermis, strongly reflect UV light, and, as the only UV-reflective element in crab spider color schemes, are the key determinant of UV-coloration. Guanine crystals are exposed through the partially UV-transmitting hypodermis and cuticle. While kynurenine is transparent to humans, it likely functions as a UV filtering pigment. UV reflectance may have evolved through a change in the metabolic pathway that allowed for guanine crystal exposure through partially UV-transmitting hypodermis and cuticle. As a whole, interactions between the cuticle, pigments and/or crystals in the hypodermis that exist in variable oxidative stages, and guanocytes combine to produce changes in the observed reflectance spectrum of crab spiders. [13]

These color change mechanisms likely evolved from ancestral crab spiders with UV-reflective abdomens or, if pre-dated by UV-absorbent hypodermal pigments, evolved through the guanine crystal exposure through a clear hypodermis. [13]

See also

Related Research Articles


The Thomisidae are a family of spiders, including about 175 genera and over 2,100 species. The common name crab spider is often linked to species in this family, but is also applied loosely to many other families of spiders. Many members of this family are also known as flower spiders or flower crab spiders.

Jumping spider Family of spiders

Jumping spiders or the Salticidae are a family of spiders. As of 2019, it contained over 600 described genera and over 6000 described species, making it the largest family of spiders at 13% of all species. Jumping spiders have some of the best vision among arthropods and use it in courtship, hunting, and navigation. Although they normally move unobtrusively and fairly slowly, most species are capable of very agile jumps, notably when hunting, but sometimes in response to sudden threats or crossing long gaps. Both their book lungs and tracheal system are well-developed, and they use both systems. Jumping spiders are generally recognized by their eye pattern. All jumping spiders have four pairs of eyes, with the anterior median pair being particularly large.

<i>Heteropoda venatoria</i>

Heteropoda venatoria is a species of spider in the family Sparassidae, the huntsman spiders. It is native to the tropical regions of the world, and it is present in some subtropical areas as an introduced species. Its common names include giant crab spider, or cane spider.


Xysticus is a genus of ground crab spiders described by C. L. Koch in 1835, belonging to the order Araneae, family Thomisidae. The genus name is derived from the Ancient Greek root xyst, meaning "scraped, scraper".

<i>Theridion grallator</i> Species of spider in the family Theridiidae

Theridion grallator, also known as the Hawaiian happy-face spider, is a spider in the family Theridiidae that resides on the Hawaiian Islands. T. grallator obtains its vernacular name of "Hawaiian happy-face spider" from the unique patterns superimposed on its abdomen, specifically those that may resemble a human smiling face. Its Hawaiian name is nananana makakiʻi. The specific epithet grallator is Latin for "stilt walker", a reference to the species' long, spindly legs. T. grallator is particularly notable because of its wide range of polymorphisms that may be studied to allow a better understanding of evolutionary mechanisms.

<i>Misumena vatia</i>

Misumena vatia is a species of crab spider with holarctic distribution. In North America, it is called the goldenrod crab spider or flower (crab) spider It is commonly found hunting in goldenrod sprays in the autumn. Males are quite small, but females can grow up to 10 mm (0.39 in) ; males reach 5 mm (0.20 in) at most. These spiders are yellow or white, and are remarkable because they have the ability to change between these two colors based on their surroundings.

<i>Nephila pilipes</i>

Nephila pilipes is a species of golden orb-web spider. It resides all over countries in East and Southeast Asia as well as Oceania. It is commonly found in primary and secondary forests and gardens. Females are large and grow to a body size of 30–50 mm, with males growing to 5–6 mm. It is the second largest of the orb-weaving spiders apart from the recently discovered Nephila komaci. The first, second, and fourth pairs of legs of juvenile females have dense hairy brushes, but these brushes disappear as the spider matures.


Milichiidae are a family of flies. Most species are very small and dark. Details of their biology have not yet been properly studied, but they are best known as kleptoparasites of predatory invertebrates, and accordingly are commonly known as freeloader flies or jackal flies. However, because of the conditions under which many species breed out, they also are known as filth flies.

<i>Cosmophasis umbratica</i>

Cosmophasis umbratica is a species of jumping spider found in South and Southeast Asia. These spiders are known for their brilliant, shiny ultraviolet light. They are members of the family Salticidae and the genus Cosmophasis. They are commonly spotted on green vegetation. C. umbratica shows extreme dimorphism when viewed under UV light: males reflect UV on all body parts that are displayed during intraspecific interaction, while females and juveniles do not reflect UV at all. It seems that C. umbratica uses this in sexual signaling. A similar phenomenon is found in some butterflies. For example, several species of Colias and Gonepteryx, both of the family Pieridae, also display sexual signaling.

<i>Amaurobius ferox</i>

Amaurobius ferox, sometimes known as the black lace-weaver, is a common nocturnal spider belonging to the family Amaurobiidae and genus Amaurobius. Its genus includes the permanently social species A. socialis, and three subsocial species, A. fenestralis, A. similis and A. ferox, all three of which have highly developed subsocial organizations.


Thomisus is a genus of crab spiders with around 150 species described. The genus includes species that vary widely in their ecology, with some that ambush predators that feed on insects visiting flowers. Like several other genera in the family Thomisidae, they are sometimes referred to as flower crab spiders, from their crab-like motion and their way of holding their front legs, reminiscent of a crab spreading its claws as a threat.

Spider Order of arachnids

Spiders are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species diversity among all orders of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat with the exceptions of air and sea colonization. As of July 2019, at least 48,200 spider species, and 120 families have been recorded by taxonomists. However, there has been dissension within the scientific community as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.

<i>Misumenoides formosipes</i>

Misumenoides formosipes is a species of crab spiders found in the US and Canada. The species' unofficial common name is white banded crab spider, which refers to a white line that runs through the plane of their eyes.

<i>Phidippus clarus</i>

Phidippus clarus is a species of jumping spider found in old fields throughout eastern North America. It often waits upside down near the top of a plant, which may be useful for detecting prey, and then quickly jumps down before the prey can escape. The spider is one of 60 species in the genus Phidippus, and one of about 5,000 in the Salticidae, a family that accounts for about 10% of all spider species. P. clarus is a predator, mostly taking insects, other spiders, and other terrestrial arthropods.

<i>Crossopriza lyoni</i>

Crossopriza lyoni is a widespread species of cellar spiders that prefer to live in or around human structures. They are commonly known as tailed cellar spiders, tailed daddy longlegs spiders, and sometimes box spiders. They all possess extremely long fragile legs that can reach up to 6 cm (2.4 in) long and a body length of that ranges from 2.5 to 7 mm. Their abdomens are distinctly squarish when viewed from the side and their carapace is more or less circular when viewed from above. They also possess two kinds of sound-producing organs and have six eyes.

<i>Pisaurina mira</i>

Pisaurina mira, also known as "nursery web spiders", is a species of spider in the family Pisauridae. They are often mistaken for wolf spiders (Lycosidae) due to their physical resemblance. Pisaurina mira is distinguished by its unique eye arrangement of two rows. 

<i>Cyclosa argenteoalba</i>

Cyclosa argenteoalba, in the trashline orbweavers genus, is a species of orb weaver in the spider family Araneidae. It is found in China, Korea, Taiwan, Japan, and Russia. Each individual has a unique appearance due to their differences in the ratio of black to silver coloring on their abdomen. Parasitic larvae are often found attached to C. argenteoalba, and the larvae are able to manipulate the spider’s behavior. During mating, female genital mutilation is common in order to increase the fitness of the male. On their webs, they often attach silk “decorations” that are thought to deter predators. Relocating to a different place to build a new web occurs frequently until they find a location with a significant amount of prey.

<i>Philodromus cespitum</i>

Philodromus cespitum is a species of running crab spider in the family Philodromidae. It is found in North America, Europe, North Africa, and parts of the Middle East and Asia. P. cespitum is a foliage-dweller, and is the most abundant species found in European fruit orchards. It acts as a biological control by preying on orchard pests. Multiple studies have been conducted looking at the effects of insecticides in fruit orchards on this species. P. cespitum is a diurnal ambush hunter and preys on aphids, insects, and occasionally competitor spider species. Males court females by tapping on the females’ bodies with their forelegs. They then insert a genital plug into the female during copulation. Unlike in many other spider species, subsequent males can mate with plugged females by removing part of the plug prior to copulation. Males discriminate among females based on virginity and plug size, and can determine these factors using the females’ draglines and plug samples.

<i>Tetragnatha versicolor</i>

Tetragnatha versicolor is a species of long-jawed orb weaver in the spider family Tetragnathidae. It is found all throughout North America, Canada, Central America, and Cuba. More specifically, in the United States, where they are most common, T. versicolor is more heavily concentrated in the New England states as well as the west coast in states like California and Washington. T. versicolor is considered a habitat generalist, and can thrive in many different environments. While they can be found in places like grasslands, wetlands, forests, etc., they prefer dryer areas like normal trees and shrubs. Unlike other spiders in the genus Tetragnatha, T. versicolor will rarely reside near aquatic environments.

<i>Thomisus spectabilis</i>

Thomisus spectabilis, also known as the white crab spider or Australian crab spider, is a small spider found in Australia and far east Asia.


  1. "Taxon details Thomisus onustus Walckenaer, 1805", World Spider Catalog, Natural History Museum Bern, retrieved 2017-06-29
  2. "Taxon details Thomisus onustus meridionalis Strand, 1907", World Spider Catalog, Natural History Museum Bern, retrieved 2017-06-29
  3. 1 2 3 4 Huseynov, Elchin F. (2007). "Natural prey of the crab spider Thomisus onustus (Araneae: Thomisidae), an extremely powerful predator of insects". Journal of Natural History. 41 (37–40): 2341–2349. doi:10.1080/00222930701589707. ISSN   0022-2933.
  4. 1 2 3 "araneae - Thomisus onustus". Retrieved 2020-11-19.
  5. 1 2 Kiany, Najmeh; Kiany, Najmeh; Sadeghi, Saber; Kiany, Mohsen; Zamani, Alireza; Ostovani, Sheidokht (2017). "Additions to the crab spider fauna of Iran (Araneae: Thomisidae)". Arachnologische Mitteilungen. 53: 1–8. doi:10.5431/aramit5301. ISSN   1018-4171.
  6. Benjamin, Suresh P.; Dimitrov, Dimitar; Gillespie, Rosemary G.; Hormiga, Gustavo (2008). "Family ties: molecular phylogeny of crab spiders (Araneae: Thomisidae)". Cladistics. 24 (5): 708–722. doi:10.1111/j.1096-0031.2008.00202.x. ISSN   0748-3007.
  7. 1 2 3 4 5 6 Levy, Gershom (1970). "The life cycle of Thomisus onustus (Thomisidae: Araneae) and outlines for the classification of the life histories of spiders". Journal of Zoology. 160 (4): 523–536. doi:10.1111/j.1469-7998.1970.tb03095.x. ISSN   0952-8369.
  8. 1 2 3 4 5 Vogelei, A.; Greissl, R. (1989). "Survival strategies of the crab spider Thomisus onustus Walckenaer 1806 (Chelicerata, Arachnida, Thomisidae)". Oecologia. 80 (4): 513–515. doi:10.1007/bf00380075. ISSN   0029-8549.
  9. Rodríguez-Gironés, M (2020). "Detectable but unseen: imperfect crypsis protects crab spiders from predators". Animal Behaviour. 164: 83–90.
  10. Théry, Marc; Casas, Jérôme (2002). "Predator and prey views of spider camouflage". Nature. 415 (6868): 133–133. doi:10.1038/415133a. ISSN   0028-0836.
  11. Théry, Marc; Debut, Martine; Gomez, Doris; Casas, Jérôme (2004). "Specific color sensitivities of prey and predator explain camouflage in different visual systems". Behavioral Ecology. 16 (1): 25–29. doi:10.1093/beheco/arh130. ISSN   1465-7279.
  12. Knauer, Anina C.; Bakhtiari, Moe; Schiestl, Florian P. (2018-04-10). "Crab spiders impact floral-signal evolution indirectly through removal of florivores". Nature Communications. 9 (1). doi:10.1038/s41467-018-03792-x. ISSN   2041-1723.
  13. 1 2 Gawryszewski, Felipe M.; Birch, Debra; Kemp, Darrell J.; Herberstein, Marie E. (2014). "Dissecting the variation of a visual trait: the proximate basis of UV‐Visible reflectance in crab spiders (Thomisidae)". Functional Ecology. 29 (1): 44–54. doi:10.1111/1365-2435.12300. ISSN   0269-8463.