Adult wasps eat sugar. That’s essentially their entire diet: flower nectar, honeydew from aphids, fruit juice, and the sugary liquid produced by their own larvae. Wasp larvae, on the other hand, eat protein, mostly in the form of chewed-up insects delivered by adult workers. This split between what adults and young wasps eat explains a lot about wasp behavior, including why they crash your picnic in late summer.
What Adult Wasps Eat
Both social and solitary adult wasps feed exclusively on sugars. In the wild, their two main sources are flower nectar and honeydew, a sticky sweet substance that aphids secrete as they feed on plants. Adult wasps also drink the sugary liquid that their own larvae produce after being fed, creating a reciprocal feeding loop inside the nest where adults bring protein to the young and get sugar in return.
This sugar-only diet means adult wasps are actually pollinators. They visit flowers regularly, and while they’re not as efficient as bees (they lack the fuzzy bodies that trap pollen), they do transfer pollen between plants as they feed. Some plant species, particularly certain orchids and figs, depend heavily on wasps for pollination.
What Wasp Larvae Eat
Wasp larvae need protein to grow, and they get it from other insects. In social wasp colonies like yellowjackets and paper wasps, adult workers hunt caterpillars, flies, spiders, and other invertebrates, chew them into a paste, and carry it back to the nest to feed developing larvae. A single large yellowjacket colony can consume thousands of insects over a summer, making wasps one of the most effective natural pest controllers in gardens and agricultural land.
Solitary hunting wasps take a different approach. Mud daubers, for example, paralyze spiders with a sting and pack them into small mud cells where they’ve laid an egg. When the egg hatches, the larva feeds on the still-living but immobilized spider. Spider wasps do the same with a single large spider per offspring. The prey stays alive but paralyzed, essentially kept fresh until the larva consumes it entirely.
Parasitoid Wasps: Eating From the Inside
Tens of thousands of wasp species are parasitoids, a life strategy where the larva develops inside or on the body of another insect and eventually kills it. These wasps are typically tiny, often smaller than a grain of rice, and they don’t sting people.
Each parasitoid species targets a specific host insect. Some specialize in aphids, others in caterpillars, and others in beetle larvae burrowing through wood. A female wasp finds the right host and lays her eggs inside it. The wasp larva then feeds on the host’s body from within, carefully avoiding vital organs to keep the host alive as long as possible. One species, Cotesia glomerata, lays an entire batch of eggs inside a single large white butterfly caterpillar. When the larvae are ready to emerge, they release chemicals that paralyze the caterpillar, then use specialized saw-like teeth to eat through its skin and spin cocoons on the outside of the body.
Another species, Hyposoter horticola, monitors butterfly eggs and lays its own egg inside just before the caterpillar is about to hatch. The wasp larva then rides inside the growing caterpillar for weeks, waiting until the host is nearly full-sized before consuming everything inside it. Because parasitoids are so narrowly focused on one host species, they’re used as biological pest control agents against invasive insects.
Why Wasps Swarm Your Food in Late Summer
If you’ve noticed wasps becoming aggressive around food and drinks in August and September, there’s a straightforward reason. Social wasp colonies reach peak size in late summer, with huge numbers of workers foraging to feed developing queens that will survive the winter. At the same time, insect prey becomes scarcer as the season winds down. With fewer caterpillars and flies to hunt, workers scavenge for alternative nutrition sources.
This is when they find your soda, beer, ice cream, and fruit. Anything sugary becomes a target. They’re also attracted to protein sources like grilled meat and sandwich fillings, since the colony still has larvae to feed. This behavior isn’t random aggression. It’s a colony running low on its natural food supply and shifting to whatever is available. The wasps pestering your outdoor meal in September are doing the same foraging they’ve done all summer, just redirected toward human food because their usual sources have dried up.
Wasps as Pest Controllers
The sheer volume of insects wasps consume makes them ecologically significant. Social wasp colonies remove enormous numbers of garden pests, including aphids, caterpillars, and flies, over the course of a season. Solitary and parasitoid wasps add to this, each species targeting its own niche of prey. In agricultural settings, parasitoid wasps are deliberately introduced to suppress pest populations without chemical pesticides.
The dual diet of wasps, sugar for adults and protein for larvae, drives this pest control. Every time an adult worker hunts down a caterpillar or spider, it’s not feeding itself. It’s provisioning the next generation. That constant demand for protein from growing larvae keeps adult workers hunting all season long, right up until the colony’s food web collides with yours at the end of summer.