Raphidioptera – the snakeflies
Tuesday, January 20, 2009 3:10:17 PM
Snakeflies are among the oddest looking of British insects. Their abdomen and wings could easily be mistaken for that of a lacewing or possibly an alderfly but their snake like head and ‘neck’ are quite distinctive. This ‘neck’ is actually an elongate prothorax, with which it can raise its head. The only other similar group with the elongate prothorax are the Mantisflies (Mantispidae) which can be distinguished by their praying mantis like modified front legs, but these are not found in the UK.
The snakeflies are the least diverse of all the Holometabolous (those with a complete 4 stage lifecycle: egg, larva, pupa and adult) orders, known as the Holometabola (Grimaldi and Engle, 2004), with the 206 known extant species divided between the Raphidiidae (with 185 species in 25 genera) and Inocelliidae (with 21 species in 6 genera) (Apsock 2002). The Raphidioptera, along with the Megaloptera (alderflies and dobsonflies) and Neuropterida (lacewings, antlions and allies) form the Neuropterida lineage. The latest cladistic studies, based on them sharing the wing articulation and ovipositor triats and molecular studies, place the Neuropterida as a sister linage of the Coleoptera, the beetles.
The distribution of the extant species of the Raphidioptera is restricted to the northern hemisphere, mainly in cold temperate regions, only occurring in the lower latitude regions of North Africa, Central America and Asia in mountainous areas. They appear to need a period of cold, near freezing temperatures to complete development (Grimaldi and Engle, 2004).
They are found in arboreal habitats, in woodland and forests of all kinds and some habitats with scattered shrubs. They are rarely found far from trees and are found from sea level up to the tree line in temperate regions, but confined to the higher altitudes with a temperate climate in the lower latitudes, typically 1000-2000m but sometimes up to 3000m in some places (Aspock 2002).
The fossil record shows the first definite occurrence in the Early Jurassic* (Engle, 2002), all it can be inferred from the fact that this specimen has many of the order’s typical features and the fossil record of the related orders that group must have originated at least as far back as the Triassic, with stem (ancestral) groups possibly as far back as the late Palaeozoic (Grimaldi and Engle, 2004). Hopefully further fossils from these times will help determine the origins of the order.
This distribution of snakeflies was much greater in the past, with extinct species found across the world with fossils known from the Early Cretaceous of South America. They were also less restricted by climate and many species occurred in the tropics in the Cretaceous (Grimaldi and Engle, 2004). But the end of the Cretaceous, the KT boundary extinction event (that is the one that killed the dinosaurs) is thought to have caused a decline in the Raphidioptera (Aspock, 1998) and although some of the tropical and subtropical species persisted into the Early Cenozoic, they were probably wiped out by the Eocene-Oligocene transition (Grimaldi and Engle, 2004), where there was a dramatic climate change, which led to the global climate getting cooler. This meant that only those adapted to the cooler temperate climates remained leaving the modern day relict assemblage of just two families with a limited temperate distribution(Grimaldi and Engle, 2004).
Adult snakeflies can be recognised by their narrow bodies with an elongate prothorax on which it can move its head and two pairs of wings of unequal size. The head is flattened, with chewing mouthparts and large compound eyes. The wings have net like veination and there is a distinct pterostigma at the anterior (front) which varies in colour. Females can be separated from the males by their long ovipositor (Gale, 2004; Grimaldi and Engle, 2004).
It is widely reported that there are 4 species of snakefly in the UK, which are listed below with their distinguishing features:
Atlantaraphidia maculicollis – a pterostigma on the forewing that starts halfway along the elongate cell behind it and extends well beyond it, with just one cross-vein.
Phaeostigma notata – pterostigma as in A. maculicollis but does not extend beyond the cell behind and usually has at least 2 cross-veins. Also a little larger than A. maculicollis.
Xanthostigma xanthostigma – a yellow pterostigma on the forewing that starts at the same point as the wing segment behind, with one cross-vein. (photos of this species can be seen here and from this thread here.)
Subilla confinis – pterostigma as in X. xanthostigma but it is brown or black. (This is the species in the photos in this article).
But Plant (1997) notes a possible 5th species, Raphidia ophiopsis, in the highlands of Scotland.
The adult snake fly feed mainly on aphids and other members of the Sternorrhycha and captive specimens have been known to take other arthropods. The eating of pollen has been observed but it is not known if it a necessary or advantageous part of their diet (Aspock 2002)
Snakefly courtship involves the use of their antennae and movements of abdomen and wings (Gale 2004). Copulation in snakeflies takes place in one of two positions: the ‘wrecking position’, where the male hangs from the female head first (usually found in the Raphidiidae), and the “tandem position”, in which the male attaches his head to the underside of the female (usually found in the Inocelliidae). These copulations last from a couple of minutes to 3 hours.
The eggs are laid by the female using her long ovipositor and will take from a few days, to up to three weeks to hatch.
Snakefly larvae are flattened and elongate, with a sclerotized (have a hard exoskeleton on the) prothorax and head which has chewing mouthparts with the rest of the organism being soft bodied (Gale, 2004). It was once believed they lived only under the bark of trees and shrubs (Aspock, 1998), but it is now known that they can be found in the upper layers of soil and possibly rock crevices (Apsock 2002). They feed on a variety of usually soft-bodied arthropods that share their habitat. The larval stage usually lasts 1 to 3 years depending on the species. The pupa of snakeflies is quite primitive and is relatively active and mobile compared to those of other orders (Grimaldi and Engle, 2004). Pupation last a matter of weeks in those that pupate in spring and several (up to eleven!) months in those that pupate in autumn and usually for those that pupate in summer.
Experiments with captive larvae have shown that without a drop in temperature (probably to around (0 C) that pupation will not occur and they will stay as larvae for several years before dying (Apsock 2002). This suggests that without a chilling snakeflies cannot complete their lifecycle and would explain why the extant species are limited to temperate climates.
See photo of a larva here here from this thread here.
Snakefly last out the winter by hibernating in either the larval or pupal stage, but never as adults or eggs (Apsock 2002).
Adult and larval snakeflies are known to suffer from parasitic mites such as Erythraeid mites, but these aren’t life threatening and are rare. The larvae however suffer from parasitism by Ichneumon wasp, particalary from the genus Nemeritis, which accounts for 95% of parasitism in the Palaearctic , within which 5–15% of a population are usually parasitized. They are also know to be parastised by braconid and chalcidid wasps.
There have been attempts to introduce Snakeflys to Australia and New Zealand for biological control of pests, but they did not become established, possibily because of the lack of a low temperature period to tripper the pupation stage.
So that is the summary of the all information available on snakeflies that I could get my hands on. The Aspock (2002) paper is a nice summary and there is a link to an accessible PDF under the reference.
I personally find them fascinating and as a predator of aphids they are a gardeners (and a foresters) friend, just like there shorter necked cousins the lacewings. So of you have or ever do come across one of these wonderful beasties do let me know.
* = for those not familiar with the geological time periods and their ages there is a handy geological time scale here http://www.stratigraphy.org/cheu.pdf
Aspock, H., 1998, Distribution and biogeography of the order Raphidioptera: updated facts and a
new hypothesis. Acta Zool. Fennica 209: 33–44.
Aspock, H., 2002, The Biology of Raphidioptera: A Review of Present Knowledge. Acta Zoologica Academiae Scientiarum Hungaricae 48 pg. 35–50.
Pdf here here.
Chinery, M. 2005, Complete British Insects, Collins, pg. 108-109
Gale, 2004, Raphioptera, website link., The Gale Group, Inc
Gale, 2004, Raphidioptera (Snakeflies), The Gale Group Inc. http://www.novelguide.com/a/discover/grze_03/grze_03_00202.html
Grimaldi, D. and Engle, M. S., 2004, Evolution of Insects, Cambridge University Press, pgs 468-480
Plant 1997 A key to the adults of British lacewings and their allies (Neuroptera, Megaloptera, Raphidiptera and Mecoptera) , Field Studies Council