With the arrival of the monsoons to southern Arizona in early July comes the arrival of many insects that rely on the summer storms to complete their life-cycles. Suddenly, the desert, quiet through the baking dry heat of June erupts with noise and the flight of insects.
A very conspicuous insect for those who are paying attention is often found clinging in bunches to mesquite trees. Aptly named the giant mesquite bug, (Thasus neocalifornicus) this 2 inch long insect completes its life cycle in 8 months, morphing into it’s sixth and final stage in early to mid-July.
The giant mesquite bug, in spite of its imposing presence poses no danger to people or the trees on which they are found. They subsist on the juices they suck from mesquite trees and seeds during the tree’s life cycle, and in spite of their large size and number, the insects do little to no harm to their hosts.
Unlike beetles and flies or butterflies, which have a larval stage which looks entirely dissimilar from its adult stage, true insects, of which the giant mesquite bug is one, go through a series of molts that always look like adult insects.
Giant mesquite bugs belong to the order Hemiptera. Hemiptera are referred to as “true” bugs. They have distinct features that set them apart from other insect orders. Hemiptera means half-wing. This is due to the presence of a unique front pair of wings, which are leathery near their base and membranous towards the tips. Most species hold their wings flat over their backs. They do not have the hard outer wing structure common in beetles.
In addition to the unique wing structure, true bugs have slender, beak-like mouthparts found at the front of the head that are usually folded underneath the insect when not in use. While most hemipterans suck the sap from plants, some are predatory, sucking the body fluids of other insects or animals (kissing bugs are a member of this order).
The giant mesquite bug is the only species in its genus that lives within the United States. The giant mesquite bug’s relatives all live further south in Mexico and Central America.
The giant mesquite bug goes through 6 successive molts through it’s lifecycle culminating in a large black flying insect. Prior molts are all wingless and start off tiny and red. The fifth molt produces a large red and white spotted wingless insect often found clinging in large bunches to the ripening seed pods of mesquite trees in late June early July.
The bright coloring of the various nymph stages is referred to as aposematic coloration and serves as a warning to predators. Giant mesquite bugs produce a chemical deterrent that changes as the insect moves through the molting process, researchers believe that this is due to differing predator threats faced by the growing insects.
Every detail of our shifting seasons brings different wildlife to the fore. These complex animals are all around us throughout the year often completely unnoticed as we humans bolt through our busy life. Sparing a moment to glance at your backyard trees can open up a whole world both incredible and beautiful.
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