Some weeks ago I wrote about the Monster Tiger Beetle (Manticora) that I had found in the savanna of Gorongosa. These insects are powerful predators, hunting grasshoppers and other small invertebrates using their enormous mandibles. The larvae of Manticora are similarly carnivorous, but rather than actively pursuing their prey the way their parents do, they are sit-and-wait predators. At that time I had not been able to see or collect Manticora larvae, but tonight I finally managed to snag one.
Like other tiger beetles, the larvae of Manticora hunt from the safety of their narrow, nearly vertical burrows in the sand. Their soft body is safely tucked inside the tunnel, and the only thing that is visible on the surface is a large, heavily sclerotized head and pronotum, both of which form a shield that blocks the access to the burrow. The mandibles of a Manticora larva are pointing upwards so that any insect unlucky enough to step on the head is instantly grabbed by its leg and pulled underground. Imagine walking down the street and stepping on one of those round metal plates that cover sewer manholes, only the plate turns out to be the head of monster, and you are instantly sucked underground – this is what it must feel to a cricket or an antlion as it is being dragged by Manticora.
I found a small aggregation of Manticora larvae on one of the sandy paths in the Chitengo camp and watched them for a little while. The aggregation consisted of 10 larvae of different ages, the smallest ones with the head diameter of about 5 mm, the largest 10-12 mm wide. A nearby lamp was attracting a lot of insects, and every 20-30 seconds an insect would invariably land near one of the Manticora burrows. The larvae clearly used their eyes to locate the prey and stretched out as far as they could out of the burrow to be ready when an insect gets really close. If the insect got within a couple of millimeters of the head, the mandibles snapped around the insect’s leg and the victim was instantly pulled underground. Interestingly, the larvae were clearly able to assess their chances of success: if the potential victim appeared to be too large to be pulled inside the burrow, rather than catching the insect’s leg the larva would flick its head and toss the insect away.
It took me a while to figure out how to extract one of the larvae out of its burrow. At first I tried digging, but the tunnels turned out to be very long, and the hard, caked soil made digging very difficult. Eventually, I used the insect’s own voracity to catch it – I gently touched the head with the forceps, and when the mandibles snapped around it I grabbed the head and pulled the larva out. It was not easy as the 5th abdominal tergite of the larva is modified into a large, spiny structure that effectively anchors the animal in its burrow. The larva’s morphology reminded me of marine polychaete worms that use a similar tactic for catching prey from the confines of their burrows.