Crawlies with Cri: Grotea californica wasp

Grotea californica wasp
(Photo by Christy Solo for the Illinois Valley News)

“My, what big antennae you have!”
“The better to sniff out small carpenter bees!”
Meet the Grotea californica wasp. Grotea are small (one-half inch), elegant parasitoid wasps in the Ichneumoid wasp family. Oh, and yes, they really do use those antennae to sniff out small bees.
We’ve met several ichneumoids before, which makes sense because there are approximately 5,000 species in the family.
With that many species parasitizing other arthropods and arachnids, most of them “specialize” in a limited number of host species. Nature knows how to balance theirself out properly so there’s always enough food for all.
Grotea cali parasitize the nests of small carpenter bees (Genus Ceratina).
You may recall that small carpenter bees build their nests in pithy burned or cut stems (stems with soft/spongy centers and hard exteriors, like blackberry). They excavate the center of the stem with their mandibles (bitey mouth parts) and use the nest for sleeping, overwintering and for egg laying in spring.
Female small carpenter bees will excavate up to 11 inches down into a stem, then lay an egg, tuck in provisions, seal off the mini chamber – rinse and repeat almost to the top of the stem.
Grotea cali females spend most of their adult lives sniffing out those hidden brood chambers. As you no doubt know, the stems of invasive Himalayan blackberries can reach “weapons grade” size and thickness; grotea cali need those extra long, extra powerful antennae to suss out those well-protected carpenter bee nests.
Now is the best time to spot grotea cali as they conduct their pithy explorations. In flight they look like a capital “T” with their red-orange bodies as the stem and those telltale antennae as a yellow cross bar.
When a grotea cali female hones in on a viable nest, she’ll use her ovipositor to drill through the outer layers of the stem and lay her own egg in with the ceratina egg.
Even as one of 5,000 species of ichneumon wasp, grotea cali manages to stand out and be unique. Not just for those lemony antennae, but for the diet of their larvae.
Grotea cali larvae aren’t strictly carnivorous like most ichneumon wasp kiddos. They will hatch before the ceratinas do, and they’ll not only eat the ceratina egg (like a typical parasitoid) but will also tuck into the pollen cake the ceratina mother left for her young.
You may recall that small carpenter bees are important spring pollinators, but don’t panic! The ratio of small carpenter bees to grotea cali is at least 50 to one, so groteas aren’t damaging the small carpenter bee population, just keeping the balance!
While adult grotea cali have no need to gather pollen, they do drink nectar, so are also pollinators and like the small carpenter bees are nectar generalists (visit many types of flowers) so they are helping to fill the same niche.