Saturday, 29 January 2011
Bristol mantids 4: The Dead Leaf mantis
Their camouflage conceals them amongst leaf litter and low bushes, where most of their prey is to be found. As a group, mantids tend to prefer sunny conditions and higher temperatures, and for this reason they are often at higher densities in farmland or other open habitats than in the shady depths of the forest. In captivity, Deroplatys need fairly high humidity as in dry conditions they are prone to problems moulting as they grow – this is a common issue with more ornamented insects of all kinds, as low humidity reduces the flexibility of the old exoskeleton.
In many insects the females are either flightless or at least reluctant fliers, and this is the usual state of affairs with mantids. Usually, males fly after nightfall, and in areas where they are found may be attracted to light. They do not seem as disoriented at a light trap as moths are though, and will often prey on other insects attracted to the light. Their chief predator at night are bats, and as with most other night flying insects they have a variety of anti-predator mechanisms to avoid getting eaten. Their hearing (via a sound detector on their thorax) is tuned to the ultrasonic calls of a bat, and when they detect a bat on a feeding approach they usually undertake extensive aerial manoeuvres to escape. It is very possible that different species have different strategies and precisely tuned hearing, to detect the commonest species of bat to prey on them, but this has been little investigated. I am not aware of any studies as to whether any species can make sounds of their own, or are distasteful to predators, but some moths can produce warning sounds to let bats know they are inedible, or disrupt their echolocation.
When disturbed by day, they have a ‘play dead’ response typical of cryptic insects. They simply fall to the ground rigid, and rely on their being indistinguishable from the leaves around them. After a few minutes, they will ‘wake up’ and climb back into the low bushes they normally live in.
One observation I heard of from someone keeping them – unlike any other mantid they will feed on other food than insects. The individual in question was offered a small fragment of banana on a toothpick, and took and ate it readily. Whether this was an artefact of captivity, or whether some mantids at least have a wider diet than has been thought, is one of the many areas of mantid behaviour that needs investigating. Mantids are after all, in essence highly specialised predatory cockroaches, and their ancestors certainly were more omnivorous than the living forms.
For a video of a Deroplatys lobata, see here: http://www.youtube.com/watch?v=I3e5eeSktQY
(picture from http://www.mantodea.info/cms/index.php?id=8&L=1)
Next week, the last and most beautiful of our mantids, The Banded Flower mantis Theopropus elegans