Dear Lord, Praying Mantises Can Actually Catch Fish

By George Dvorsky on at

Praying mantises are what scientists call “generalist” hunters, meaning they eat pretty much whatever they want. Despite their eclectic taste, however, no one has ever seen a praying mantis eat fish—until now.

These formidable insects have been observed to eat other insects (especially fly-like bugs), lizards, frogs, snakes, turtles, mice, and even small birds (namely hummingbirds and brown creepers). Mantises are able to do so on account of their excellent 3D vision and powerful front legs, which they use to snatch unwary prey.

So yes, their taste in prey is diverse, but apparently it’s even more diverse than we thought. Last year in India, a team of scientists led by Roberto Battiston from the Museums Canal di Brenta in Italy watched as a single mantis munched on nine guppy fish over several days. The resulting paper, published yesterday in the Journal of Orthoptera Research, is now the first to document fish-eating behaviour in a mantis species. The unprecedented observation is changing what we know of praying mantises in terms of their versatility, physical capabilities, and intelligence.

The artificial pond with the male praying mantis sitting on a leaf to the right-hand side of the photo. (Image: Rajesh Puttaswamaiah)

Observations of this 2.2-inch-long male mantis (Hierodula tenuidentata) were made in a private roof garden in Karnataka, India. The garden may be artificial, but the researchers say it’s a very close approximation of mantises’ natural habitat, featuring wasps, butterflies, spiders, and several planters. The team observed the mantis as it hunted and devoured the guppies, also known as rainbow fish, in a pond, which it did for five days in a row. In total, the mantis ate nine fish, at a minimum rate of two per day. Here’s what the scientists saw, as they describe in the new study:

In seven cases, the mantid started eating from the tail. On a single occasion, he started from the head and on another, from the top side. On the first four of the five days, the mantid was observed to hunt and devour two fish. The second fish was hunted within 10–30 mins of consuming the first one. After the fifth day, the mantid disappeared and was not observed again at the pond.

The feedings were not manipulated by the observers and occurred without any human interference, according to the paper. The mantis reached the fish by perching on leaves of water lilies and water cabbage.

That mantises prey on guppies is interesting in and of itself, but there’s a lot more to this stunning discovery.

First, it shows how amazingly adaptable these insects really are. Fish don’t move like lizards, locusts, hummingbirds, or flies, yet this mantis was able to snatch the guppies when they swam near the surface. The mantis devoured nine of the 40 fish in the pond over a five-day period, “showing the potential for a single invertebrate to have a strong impact on the fish community and, since guppies, like many other small fish, are active predators of aquatic insects, indirectly on the whole pond ecosystem,” the authors write. Importantly, this behaviour was seen in just one individual; more observations will be needed to know whether this was some kind of freaky, isolated incident.

Come to me, my pretty: The mantis shown ready to strike. (Image: Rajesh Puttaswamaiah)

Second, it appears that mantis vision is even better than we thought. The feedings occurred from sunset at 6:30 p.m. to 12:30 a.m. The large compound eyes of mantises are sensitive to movement, and adapted primarily to daylight conditions. This mantis, however, was able to see the fish during both dusk and night conditions, while also having to overcome and adapt to the refraction of light through the water. Male mantises tend to be very active during the night, the authors write, but these fishing events “suggest further visual abilities of mantids that should be investigated.”

Lastly, this observation tells us something new about mantis intelligence. After discovering the fish and developing a proficient hunting technique, the mantis came back repeatedly to the garden to feed. This strongly suggests that the mantis learned from the experience, figuring out where and what to hunt. This insect, it would appear, is not a mindless automaton driven by basic instincts or environmental cues, like ants following a pheromone trail (nothing against ants, they’re also awesome).

This strange tale, whether it represents a one-off event or a recurring mantis behaviour, points to the remarkable abilities of a truly fascinating—and horrifying—predatory insect. [Journal of Orthoptera Research]