 | This article includes a list of general references, but it lacks sufficient corresponding inline citations .(February 2008) |
Cave-dwelling insects are among the most widespread and prominent troglofauna (cave-dwelling animals), including troglobites, troglophiles, and trogloxenes. As a category of ecological adaptations, such insects are significant in many senses, ecological, evolutionary, and physiological.
A cave is an unusually well-defined ecological habitat in terms of its nature, time, and place. Accordingly, it is not surprising that a number of insects permanently inhabit caves, especially at the deepest levels, and are markedly specialised for niches in some of the extreme conditions. These are the true cavernicole species; troglobites rather than troglophiles or trogloxenes. These include; spiders and insects.
Cavernicolous insect species rarely are adapted to move from cave to cave, so each species or community generally will be restricted wholly to certain caves or cave systems each, and commonly will have evolved in their respective home cave systems. Exceptions commonly are those that have been carried by mobile vertebrate trogloxenes or troglophiles, though in some cases a number of populations may have evolved from a single mobile troglophile population. Caves tend to be geologically short-lived, so most of the specialised adaptations are correspondingly young in evolutionary terms and to have arisen rapidly and in parallel from similar ancestors that began as similar troglophiles in separated caves. Many insect troglobites are Orthopteran, Collembolan, or Blattodean, for example, and given the nature of their open-air ancestral species, it would be in no way surprising that where a cave becomes available, it soon is invaded by opportunistic troglophiles that may be widely distributed and may evolve similarly in separate caves in different areas. [1]
Caves also appear to have become the last refugium for many ancient types of insects, which are no longer found free in the open in surrounding regions. Such cave fauna thus represent, at least in part, relicts. It does not follow that they had been in those particular caves since ancient times though. For example, modern troglobitic Onychophora had not been occupying their current caves since the Carboniferous period but had entered new caves comparatively recently and flourished by exaptation.
Once adapted to troglobitic existence, cave insects become specialised and dependent on the cavernicolous conditions; when suddenly exposed to the outside world, they are likely to succumb rapidly.
True cavernicolous species, troglobites, include many animals apart from insects. There are various troglobites among the planarians, Oligochaeta, Polychaeta, leeches, Mollusca, and fishes. Troglobitic Crustaceans include species of Amphipoda, Cladocera, Copepoda, Decapoda, Isopoda, and Syncarida. Many troglobites are predatory, including Chilopoda, Acari, Opiliones, Chernetidae, and spiders.
Troglobitic insects include Apterygota such as Campodea and various Collembola. There are many species of beetles in families such as Carabidae, Curculionidae, Leiodidae, and Silphidae. Some Orthoptera are troglobitic and some are trogloxenic. The order Blattodea includes troglobites, and so do the Trichoptera and Diptera.
The cave dwellers fall under one of the following categories:
The climate in deep caves typically is without distinction of day and night, But insects have a sleeping pattern and not many are affected even by the passage of the seasons. Violent winds and storms are unknown, though there may be steady air currents under some circumstances. Humidity is roughly stable. Communications with the outside world only occur under special conditions such as floods and exceptional droughts. Where streams pass through caves or water seeps in, they commonly are important sources of nutrition.
Trogloxenes are important to cave ecology, because they commonly feed outside and import material that serves as food when they return. Insect species such as some butterflies, flies, and beetles over-winter in caves, and casualties remain as food. Cavernicolous bats, being trogloxenes, are major ecological factors in some caves where they spend their daylight hours, and some species such as Mexican free-tailed bats provide massive deposits of organic matter, mainly in the form of faeces and carcasses.
Other trogloxenic animals include vertebrates such as bears, hyenas, other predators, reptiles, oilbirds, cave swiftlets and even humans, that enter for short term shelter or for hibernation. Most of them contribute organic matter rather than consuming it, and are important resources for troglobitic insects, many of which actually specialise in reliance on particular species that are long-term regular visitors. The cave environment thus is characterised by absence, restriction, or attenuation of certain factors such as light, circadian or seasonal stimuli, living space, freedom of movement, or abrupt contrasts in temperature and humidity. Other items may depend on local conditions; for example, most caves provide little available food and some provide little water, whereas some provide perennial water or quantities of dung so great as to support ecological stratification, with organisms preying on other organisms that live in turn on different stages of the original product.
The ultimate sources of nearly all food in caves are outside the cave. Running water and air currents carry in carcasses and other organic detritus. Fungi and bacteria that develop on this material provide food for many cave dwellers. Bat guano represents another source. Lepidoptera that enter caves for sleeping are preyed upon by troglobitic Orthoptera, largely Tettigoniidae and Gryllidae. The cavernicolous Collembola feed on colloidal matter in the water or dust borne on the surface tension. The insects and similarly sized invertebrates are food for spiders and Myriapoda. Most such activities go on in darkness, except close to the outside, or where certain microbes or insects such as Arachnocampa provide bioluminescence, even if only to attract prey.
In individual caves, the most conspicuous and perhaps most ubiquitous peculiarity of insects, as with other troglobites, is the reduction of body pigmentation. This does not apply to all cavernicolous insects. It is particularly marked in Coleoptera. The reduction or total loss of body pigmentation is correlated with the absence of sunlight. A second peculiarity is the reduction of eyes in all cavernicolous species. This contrasts with most nocturnal or crepuscular species, in many of which there is a strong tendency to adapt to low light levels by responding to selection for large, highly sensitive eyes.
A form of adaptation common to many cave insects as well as some external predatory species, is elongation of appendages, especially the antennae, palps and forelegs that assist in precise location of prey before striking. Many also bear elongated sensory organs, typically setae, as for example, in the beetle Scotoplanetes arenstorffianus, in which there are well developed setae, including on the elytra and also supraorbitally, but the eyes themselves are absent. [3] from Herzegovina. In contrast, none of the free-living related carabids have such sensory setae on the elytra. Troglobitic insects commonly have no functional wings, and many have no wings at all. One exception is Troglocladius hajdi (family Chironomidae), which has strongly reduced eyes consisting of only 0–4 ommatidia, yet have well-developed wings and is able to fly in total darkness. [4] Among the cave beetles the elytra may be retained as sclerotised bodily protection, but the hind wings, that are used for flight in most beetles, are non-functional or absent.
Some important cave insects from Europe include the following: Paraoalyscia wollastoni, Bathysciola fauveli, Trechus (Trichaphaenops) sollandi, Royerella villaridi, Trechus (Trichaphaenops) angulipennis, Trechus (Duvalius) pilosellus stobieckii, etc. The beetle Leptodirus hochenwartii , found in the Postojna cave system in Slovenia, was the first animal to be recognized as a true cave dweller. [5]
The cave insects found in the Atlas Mountains include blind Trechus jurijurae , Aphaenops iblis , Nebria nudicollis with very long antennae and legs, the staphylinids Paraleptusa cavatica and Apterophaenops longiceps , and the curculionid Troglorrhynchus mairei . The carabid Laemostenus fezzensis is a troglophile. Neaphaenops tellkampfi occurs in caves in Kentucky. The American stenopelmatid Hadenoecus subterraneus is recorded from Kentucky caves. The remarkable carabid Comstockia subterranea is a true cave species found in Texas. The exclusively cave-dwelling silphid Adelops hirtus occurs in Kentucky caves and has very minute, unpigmented, atrophied eyes.
The Hawaiian islands have a significant number of endemic cave insects that inhabit lava tubes, including several blind planthoppers that feed on ʻōhiʻa roots (Oliarus polyphemus, Oliarus priola, Oliarus kalaupapae), a lava tube water treader (Cavaticovelia aaa), and several species of Caconemobius cave crickets.
A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word cave can refer to smaller openings such as sea caves, rock shelters, and grottos, that extend a relatively short distance into the rock and they are called exogene caves. Caves which extend further underground than the opening is wide are called endogene caves.
Beetles are insects that form the order Coleoptera, in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 described species, is the largest of all orders, constituting almost 40% of described insects and 25% of all known animal species; new species are discovered frequently, with estimates suggesting that there are between 0.9 and 2.1 million total species. Found in almost every habitat except the sea and the polar regions, they interact with their ecosystems in several ways: beetles often feed on plants and fungi, break down animal and plant debris, and eat other invertebrates. Some species are serious agricultural pests, such as the Colorado potato beetle, while others such as Coccinellidae eat aphids, scale insects, thrips, and other plant-sucking insects that damage crops.
The Amblyopsidae are a fish family commonly referred to as cavefish, blindfish, or swampfish. They are small freshwater fish found in the dark environments of caves, springs and swamps in the eastern half of the United States. Like other troglobites, most amblyopsids exhibit adaptations to these dark environments, including the lack of functional eyes and the absence of pigmentation. More than 200 species of cavefishes are known, but only six of these are in the family Amblyopsidae. One of these, Forbesichthys agassizii, spends time both underground and aboveground. A seventh species in this family, Chologaster cornuta, is not a cave-dweller but lives in aboveground swamps.
Dermestidae are a family of Coleoptera that are commonly referred to as skin beetles. Other common names include larder beetle, hide or leather beetles, carpet beetles, and khapra beetles. There are over 1,800 species described.
Entomobryidae, sometimes called "slender springtails", is a family of springtails characterised by having an enlarged fourth abdominal segment and a well-developed furcula. Species in this family may be heavily scaled and can be very colourful. The scale-less Entomobryidae are commonly caught in pitfall traps around the planet, and also occur in canopy faunas high up in trees. There are more than 1700 described species in Entomobryidae.
Troglofauna are small cave-dwelling animals that have adapted to their dark surroundings. Troglofauna and stygofauna are the two types of subterranean fauna. Both are associated with subterranean environments – troglofauna are associated with caves and spaces above the water table and stygofauna with water. Troglofaunal species include spiders, insects, myriapods and others. Some troglofauna live permanently underground and cannot survive outside the cave environment. Troglofauna adaptations and characteristics include a heightened sense of hearing, touch and smell. Loss of under-used senses is apparent in the lack of pigmentation as well as eyesight in most troglofauna. Troglofauna insects may exhibit a lack of wings and longer appendages.
Trogloxenes or subtroglophiles, also called cave guests, are animal species which periodically live in underground habitats such as caves or at the very entrance, but cannot live exclusively in such habitats. Among many scientists, trogloxenes and subtroglophile have slightly different but closely related meanings, with the former covering species that are occasional visitors to underground habitat and the latter species that live more permanently there, but have to go outside. Both these are in contrast to troglobites, which strictly live in underground habitats.
Neocicindela tuberculata is a species of tiger beetle in the family Cicindelidae, endemic to New Zealand. Its common names include common tiger beetle, moeone, and papapa, and in its laval stage penny doctor, butcher boy, kapuku, kui, kurikuri, moeone, and muremure. Neocicindela tuberculata was the first carabid beetle described from New Zealand. The species can run as fast as 5 miles per hour and are considered to be the fastest running beetles. Adult species prefer clay banks in summer and are good predators when in comes to insects.
Texella reddelli, the Bee Creek cave harvestman, is a rare species of troglobitic harvestman that was added to the United States endangered species list in 1988, at the same time as six other species native to the karst ecosystem in Travis County and Williamson County, Texas, USA. They inhabit areas with near 100% humidity and constant temperatures, and they prey on springtails. Research on these creatures has been difficult since they can only be found underground. Their distribution is limited and unknown reproductive rates mean that it is possible they are especially susceptible to habitat destruction and other threats. Texella reddelli are found on both the North and South sides of the Colorado River.
The Kretschmarr Cave mold beetle is a small mold beetle.
Leptodirus is a cave beetle in the family Leiodidae. The genus contains only the single species Leptodirus hochenwartii. It is a true troglobite, endemic to Slovenian, Croatian and, partly, Italian caves.
Radford Cave, in Hexton Wood, near Hooe, Plymouth, Devon is a small phreatic cave of some ecological interest. It has been known to speleologists and others for many years and a plan was published in 1953.
Trogloraptor is a genus of large spiders found in the caves of southwestern Oregon. It is the sole genus in the family Trogloraptoridae, and includes only one species, Trogloraptor marchingtoni. These spiders are predominantly yellow-brown in color with a maximum leg span of 3 in (7.6 cm). They are remarkable for having hook-like claws on the raptorial last segments of their legs.
Subterranean fauna refers to animal species that are adapted to live in an underground environment. Troglofauna and stygofauna are the two types of subterranean fauna. Both are associated with hypogeal habitats – troglofauna is associated with terrestrial subterranean environment, and stygofauna with all kind of subterranean waters.
Troglomorphism is the morphological adaptation of an animal to living in the constant darkness of caves, characterised by features such as loss of pigment, reduced eyesight or blindness, and frequently with attenuated bodies or appendages. The terms troglobitic, stygobitic, stygofauna, troglofauna, and hypogean or hypogeic, are often used for cave-dwelling organisms.
Biospeleology, also known as cave biology, is a branch of biology dedicated to the study of organisms that live in caves and are collectively referred to as troglofauna.
Paraphrynus is a genus of whip spiders, also known as tailless whip scorpions, of the family Phrynidae. It is distributed from the southwestern United States to Central America, including several Caribbean islands. Most species are endemic to Mexico.
Anisodactylus binotatus is a species of ground beetle native to Europe. It was discovered as being introduced to Canterbury, New Zealand in 1938. Anisodactylus binotatus is a species of Carabidae, also known as the ground beetle family. Although this species of beetle has no official recorded common names, literature from England refers to it as the common shortspur beetle.
Mecodema howitti, termed the Large Banks Peninsula ground beetle, is a carnivorous forest ground beetle in the genus Mecodema. It is endemic to Banks Peninsula, Canterbury, New Zealand, and is the largest of the 16 carabids found in the area.