Wild Side: Predation occurs in many forms in the natural world

A preying mantis dines on a grasshopper lunch.
Photo by Matt Pelikan

A preying mantis dines on a grasshopper lunch.

It’s no news, of course, that the natural world runs on predation. The diet of many animals consists almost entirely of other, usually smaller, species. But even among so-called herbivores, eating mainly plants, many species will dine on meat if a good opportunity arises: white-footed mice, for example, love caterpillars of certain species. The science of catching, and of avoiding being caught, is highly developed on the Wild Side, and as an observer in the field, I find that watching this lethal game is endlessly captivating.

Often, predation happens in a way that’s easily overlooked. The swarms of migrating tree swallows now moving around the Island, for example, are fueling up largely on berries. But they’re also taking flying insects in large numbers, and if you can carefully follow a single swallow, you’ll readily spot the sudden change in direction as this sharp-eyed aerial predator zeroes in on and engulfs a small fly or other insect.

Indeed, with a large size disparity between predator and prey, insectivorous birds take scores or hundreds of prey items a day. The life of a songbird feeding nestlings, or of a migrant warbler stopping on the Vineyard to gain weight before the next stage of its journey, is a matter of nearly constant shopping. The bustling of these birds seems innocuous enough until you catch a glimpse of what they’re carrying, or realize that each probe of the beak represents another tiny spider or caterpillar down the hatch.

But sometimes predation gets more dramatic and personal. Last Saturday, for example, I patrolled my front yard, hoping to get a good photograph of a grasshopper species that has been fairly common there of late. I found one, eventually, but a preying mantis had found it first. Immobilized in the spiny grasp of the much larger mantis, the grasshopper had no chance, and I watched as the mantis began the process of disassembly.

Surprisingly, dinner began with the legs. It had eaten or removed the large hind legs before I discovered it. Then, starting with the foot, the mantis methodically ate one of the grasshopper’s middle legs. Then it ate another, then the two front legs, each taking only a matter of seconds. From the hole left where the legs had been attached, the mantis began pulling out the contents of the grasshopper’s body — mainly, it looked like, a layer of fat the grasshopper had stored. Then it enlarged the holes, snipping away the grasshopper’s exoskeleton with incredible precision and drawing out more of the smaller insect’s viscera. In less than ten minutes, the process was done: the mantis had consumed the entire grasshopper and relaxed its posture to digest.

The next day, searching for interesting insects in the State Forest, I noticed a glossy black wasp dragging a fat spider, several times the size of the wasp, across the bare sand of a fire lane. Paralyzed by a sting from the wasp, the spider was destined for a burrow in the ground. In a grisly maneuver that is surprisingly common in the insect world, the wasp would lay an egg on or near the paralyzed prey, which then serves as a food source for the wasp larva as it hatches and grows.

Closing in to photograph the wasp and its prize, I accidentally disturbed the triumphant predator, which wisely kept in mind the risk of becoming prey herself. Leaving the spider behind, she flew in widening circles, while I sat motionless, waiting for her to calm down. Despite the vigorous evasive maneuvers, the wasp never lost track of the immobile spider. After a minute or two, evidently satisfied that my now-stationary bulk didn’t represent a threat, the wasp zeroed in on her prey, walked around it in a businesslike manner, grabbed the front end, and resumed pulling on the original heading.

Fairness doesn’t figure on the Wild Side. Falcons, swift hawks optimized for catching smaller birds, love to sit on a prominent perch near the shoreline at this season. Why? Because sooner or later, a migrant songbird that has ended up over the water will head for land. Exhausted, with the unforgiving sea behind it and a falcon between it and the safety of land, the songbird has no chance.

And that’s the point, of course, from the falcon’s perspective. When you make your living by eating your neighbor, there is no room for sentiment and no reason to settle for anything other than the easiest kill. It’s a harsh system, and I have to say it leaves me a little uneasy at times. I observe wildlife because I like it, and even in the case of an insect, seeing one of my friends suffer is unnerving.

But I can’t not watch. The behavior of predators is varied, clever, and fascinating, and the acts of killing and consuming are dramatic. Predation is the real thing, a central process on the Wild Side.