Common name: Aphid wasps
Family: Crabronidae (subfamily Pemphredoninae)
Nest type: Resin (sap and pitch), sometimes supplemented with bits of debris, both for walls between nest cells and for nest plugs
Size: 1/4 to 3/4″ long, depending on the species
Nest tunnels used: Depending on the species, tunnels from 1/16″ to 7/16″
Looks like: Smooth-bodied, shiny, slender black wasp
Wasps have a bit of a reputation, to the point that “waspish” is synonymous with “nasty”. Most people will destroy a wasp’s nest without hesitation, even if they’re friendlier with insects than the average bear. Wasps from the Passaloecus genus, however, are doing their best to get into humans’ good graces by preying on aphids, those despised little bugs that can destroy an entire garden. Passaloecus species stock their nests with enough aphids to feed their larvae until maturity, which is enough reason in itself to greet them with welcome rather than fear. They also supplement their diet by sipping on honeydew, which is the sugary secretion that aphids make.
You can find as many as 7 Passaloecus species in Colorado, guarding your garden from early spring to late summer. Their lack of hair is a solid clue they’re carnivorous wasps rather than pollinating bees, but as there are some smooth-looking bees, it’s not always the best way to tell—especially when they’re buzzing around.
DID YOU KNOW: There are many other wasps that prey on aphids. Some, like Aphidius, are parasites that actually lay eggs inside the aphid’s body, which then feed on its insides and, once they grow to maturity, the baby wasps burst out of the now-mummified aphid body. Just like in Alien.