When the mantises broke into their bodies, they found no plant matter in their guts. As a result of these body-snatchers, the caterpillars had barely eaten any milkweed. The third was heavily infested by a fungus. The other three were all harbouring parasites! Two of them contained the larvae of a tachinid fly, which were slowly devouring them from the inside out. Rafter noticed one pattern that supports this second idea: she watched their mantises eating 21 caterpillars, and they only gutted 18 of them.
And by happy coincidence, that reduces the total amount of poison that it consumes. So perhaps the mantis is just feasting on the richest tissues and discarding the nutrient-poor ones. These organs tend are usually filled with chewed-up plant matter and contain 58 percent less nitrogen than other tissues. Maybe the mantis can tolerate these processed forms, but is trying to avoid the originals in the guts.Īlternatively, the mantis might just find the guts distasteful, or not worth the effort.
This suggests it’s processing or breaking down the cardenolides that it gets from the milkweed before storing them in its other tissues. The caterpillar’s body has around three times as many types of these chemicals as its guts, but at lower concentrations. The mantis might only be vulnerable to some cardenolides and not others.
