Sunday, 16 January 2011

Bristol Mantids 2: Back to basics

From the decidedly odd-looking Violin Mantid, this week I will discuss one of the more usual-looking mantids, the African Bush mantis Sphordromantis viridis. A native of sub-Saharan West Africa, this species is a typical generalist predator, taking insects of all kinds from crickets to butterflies. Size is no object – they will happily tackle prey nearly as big as themselves. They are not as large as some mantid species, growing around 6-8cm long.

The identification of the various species of Sphodromantis, particularly those in the pet trade, is very difficult owing to the large number of very similar species in the genus, and without a definite location of origin pinning down which species is involved may be practically impossible. To make matters worse, the species are often quite variable in appearance, especially colour, so for example the one we have, although its’ specific name means ‘green’, may also be a dull brown.

How the different colour patterns arise is one of the many factors in ecology of mantids which has not been studied. This problem is by no means confined to mantids, and affects practically all insects except those which affect agriculture. For most insects, the total knowledge of the species could be summed up as ‘it grows to x mm long and lives in y’.

This of course means that there is considerable opportunity for anyone – even a school – to do research on many species. For Sphodromantis colours, possible influences on colour could be genetic, temperature, ambient humidity, day (or night) length, or diet among other factors. Light may also be significant – most insects can detect UV light, and most captive invertebrates are kept in quarters which are lit with standard incandescent bulbs which do not produce much of these frequencies. Rearing nymphs under different lighting, temperature, or humidity conditions could make an interesting class project.

Another key area of mantis ecology is the predators that feed on mantids and regulate their populations. Amongst vertebrate predators, frogs, lizards, and birds are probably the most important animals to feed on mantids, but their superb camouflage and solitary lifestyle means that they are only taken by chance as an insectivorous animal comes across them. Probably more important are invertebrate predators, especially spiders and ants. These are often too small or too fast to be easily caught by a mantid, so they are a bigger threat.

Even more important are parasitoid flies and wasps. These attack most insect eggs, and will certainly attack mantid oothecae, and probably the adult mantids as well. Unfortunately, these are even less studied than the mantids, so anyone keeping mantids, or who observes a wild found oothecae, should certainly try to preserve any parasitoids that emerge and if possible make them available to a museum or scientific institution.

Next week – a giant mantis, Plistospilota

(image from wikipedia)

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