Sunday, 23 January 2011
Bristol mantids 3: The biggest of them all
Originating from Guinea (hence the specific name) and neighbouring countries in West Africa, Plistospilota is another generalist hunter, prowling the ground and shrubs for anything it can catch. Its formidable forelegs means it can give draw blood if unwisely handled even from a human being, and if annoyed it will warn off the predator with a rather spectacular threat display, as the picture at the head of this post shows.
There are three basic hunting strategies followed by mantids. The most ancient form of hunting is a generalist prowling for any suitable insect, and is still followed by many species. Some have turned to a more cursorial lifestyle, and chase down and pounce on any prey they see ahead of them. This lifestyle is especially found in desert species, but mantids that typically live on the trunks of trees or large branches may also behave this way. Cursorial mantids can be identified by their unusually long legs and more active behaviour. Finally there are the ambush predators. These wait, protected by their exquisite camouflage, for insects to come to them. The most famous example of this type of mantid is the orchid mantis. These mantids habits of waiting on flowers means that butterflies have to be very careful – in the butterfly house you can see the flower feeding butterflies often spending several seconds inspecting a flower to make sure there are no mantids or other predators waiting before stopping to feed. Ambush mantids need a different visual system, as they scan for prey in three dimensions whereas the other species look only ahead and to either side as they move around their habitat.
Mantids appeared fairly late in earth history. Although their presumed ancestors, the cockroaches (which also gave rise to the termites) are some of the oldest known insects, dating back to the Carboniferous, the oldest fossil mantids are first known from the Cretaceous, This is also the time when the first fossil termites are known, and it is probably no coincidence that these major insect groups (plus others such as the bees, ants, and butterflies) all appeared with the first flowering plants. The diversification of the angiosperms triggered an entomological revolution, as the flowering plants made a whole host of new foodplants, pollen and nectar sources, and (as a side effect) new prey available. This is an aspect of earth history that often gets overlooked in the more spectacular studies of dinosaurs and other fossil vertebrates – because insects fossilise much more rarely, we assume the insect fauna has a less interesting and complicated history. Who knows what major groups may have appeared and disappeared since life appeared on land, having key influences on ecosystems, but disappearing without trace?
For a video of a Plistospilota in action, see here: http://www.youtube.com/watch?v=gnnTtT2iMjk&feature=related
For more on mantis evolution, see here: http://www.mantodearesearch.com/PDFs/Svenson%20and%20Whiting%202004.pdf
(image at top from http://www.bugnation.co.uk/viewtopic.php?f=336&t=45729)
Next week: a master of disguise, Deroplatys the Dead Leaf mantis