Earlier this spring we talked about the mason bees, Osmia and Hoplitis, that made plugs from chewed vegetation. Then, the last Plugs & Bugs post focused on Megachile that use whole leaf or petal pieces. Now we are combining the two to look at the Megachile that make plugs from Chewed Vegetation.
We have multiple Megachile species in the Front Range that plug with chewed vegetation, but unlike the Megachile that use whole leaf pieces to plug the nests and line their cells, the Megachile we are focusing on this week complete their nest plugs with chewed up leaf pulp and do not line their cells with leaf pieces. Their bodies are long and thin with white stripes made of hairs. Chewed vegetation plugs, like minced up leaves, start out as bright green, but as they dry they discolor and often pull away from the edges of the nesting tunnels.
Megachile (Sayapis) pugnata is a rather pugnacious species. They are not aggressive towards people, but they do quarrel a bit with their neighbors. On an active afternoon, they can sometimes be seen just hanging out in their nests, protecting their turf, rather than foraging. A bee that doesn’t defend her nesting tunnel may lose it to a larger, more persistent female. M. pugnata is variable in size, but tends to have a large head with a spine on the lower edge of its cheek. They typically nest in the column 2 tunnels, though large individuals will nest in the column 1 tunnels.
In creating their nest plugs (and cell partitions), they start with several irregularly shaped pieces of leaf, but then cover this with chewed up leaves. They will often add soil particles to the chewed vegetation making it appear darker and more grainy than chewed vegetation alone, but you should still be able to detect some green color and fibrous quality . M. pugnata often recess their nest plugs a good 1/2 inch or more, making them difficult to see and identify (and photograph)!
Megachile (Chelostomoides) subexilis is a somewhat smaller, less feisty, bee that nests in the column 2 tunnels. This species often begin their nest plug not with a leaf piece or two, but rather with a base of resin. They top off their plugs, flush with the face of the nest block, with bright green chewed vegetation, no dirt included. This species is multi-generational here in Colorado. After emergence holes appear in the plug, one of the daughters (or a neighbor’s daughter) will clear out the nest remnants and reuse the tunnel herself.