Philanthus gibbosus

While the general range of P. gibbosus size is 10–12 mm in length, females are usually closer to the smaller end of the scale. Female P. gibbosus have more yellow coloration on the head than do the males of the species.[2]

Female P. gibbosus

The males of P. gibbosus resemble the females very closely, but the most notable difference is the significantly reduced presence of yellow spots on the head. This is opposite of the usual pattern observed within the order Hymenoptera. Most commonly, the males in hymenopteran species have an excess of yellow spots on the head while females lack spots.[2]

P. gibbosus larvae

The cycle begins around the first or second week of June when the early pioneers start searching for a nesting site.[4] Even though the searching starts as early as June, the actual digging of the new nest may not start until the first or second week of July. By early July, however, nest construction is in full swing. Females spend about three weeks completely devoting themselves to provisioning and laying eggs, but once the season is over, they die.[2]

In the middle of July, the progeny of the first brood begin to emerge. The emergence of larvae continues to rise linearly through the last week of August. A majority of these new progeny have already dispersed to lay new eggs and died off by early September. The few members of the new progeny that remain continue laying eggs for another two weeks, but will die by October, likely due to changes in climate around that time. This second generation of larvae survive the winter by remaining in their cocoons from October through April. In April, the second generation changes into pupae and emerge in May. Those that emerge in May are the wasps that are responsible for searching for a new nesting location in June.[2]

Various burrow architectures of P. gibbosus

P. gibbosus is a solitary wasp that nests in the ground. Several individuals have been observed to cohabit a single burrow at a time. However, there is evidence that suggests that while females tend to occupy the parental nest for a mere several days of their lives, the males will sometimes inhabit the nest for their entire life. After the few days in their original nest, the females will disperse to new nests. However, one single female may continue to inhabit and expand the original nest. On very rare occasions, two females may provision the original nest at the same time for a very brief period. Evidence suggests that P. gibbosus may be representative of a unique stage in presociality in which temporary communal nesting occurs at certain phases of the nesting cycle, in spite of the species' usual solitary living.[6]

Because P. gibbosus is a solitary wasp species, there is not much need for intra-species communication. However, when mating, males are responsible for marking the territory surrounding the nest with pheromones as a means of warding off other competing males from mating with the female in the nest. These pheromones are the main form of intra-communication, specifically between the different, individual males of P. gibbosus.[7]

During the main season of its activity, May through September, the entrance to the nesting sites of P. gibbosus can be characterized by the scattered heaps of sand or soil around their supporting structure, usually bricks or tree roots. The sand heaps are very low and spread out. In building these sand heaps, females can be observed backing out of the burrow with moist sand or soil that is spread around into the heaps using jerks of her front legs. While burrowing, P. gibbosus stands on its hind legs. In order to dig the actual burrow, P. gibbosus uses its tarsi and mandibles to dig a shaft that is at least two feet in length. The shaft culminates in an oval shaped cell in which eggs are provisioned. Other oval shaped cells line the shaft which are smaller in size and contain the skeletons of other bees that were killed and fed to the larvae as nutrients.[2]

Female P. gibbosus full body coloration

P. gibbosus is a part of a mimicry group with a wide variety of other wasps that also exhibit black and yellow banding and coloring. It has been observed that mimicry is high in spring and early summer, generally absent in midsummer, and infrequent in late summer. This implies that some members of the mimicry group, including P. gibbosus, may be selected to avoid the midsummer season when insectivorous birds are abundant and have not yet learned to avoid the models which the mimics resemble.[9] The colony cycle of P. gibbosus lines up with this scheduling in such a way that minimizes the amount of predation the species faces.

While P. gibbosus does not camouflage with its surroundings, it exhibits a black and yellow chitin coating that serves as a warning to other predatory species. This coloration pattern that is characteristic of many species of wasps is a somewhat universal sign that an organism stings and should, as a result, be avoided in predation.[6]

P. gibbosus spend a significant amount of time loitering around flowers and other plants in search of insect prey to feed their young, most often bee species. Some common species that P. gibbosus predates include the beetle Cucochodaeus sparsus and sweat bees Augochlora pura and Lasioglossum cinctipes (formerly Evylaeus arcuatus).[2]

Predation of a bee by P. gibbosus

P. gibbosus is notable in that it stings its prey in a membranous location on the ventral surface of the abdomen where the venom is quick to incapacitate many major, voluntary muscles. The paralyzing effect of the injected venom is likely due largely in part to a block of the somatic neuromuscular transmission. It has also been established that the venom is not limited exclusively to the natural prey, the honey bee, but also in many other insect species belonging to different orders, including spiders. Only P. triangulum itself and a digger wasp that preys on P. triangulum are immune to the venom.[10] However, the sting does not kill the prey. The prey may attempt to sting in return, but P. gibbosus always grabs the prey in such a way that the well-armored portions of the body are presented, thus protecting P. gibbosus from a retaliation by the prey. P. gibbosus then carries its paralyzed prey back to an oval cell in its nest for temporary storage until it is later used in the laying of an egg.[7]

Although P. gibbosus feeds on insects, they are also prey for certain insects as well. Predatory insects for P. gibbosus include praying mantis, robber flies, and dragonflies. Sometimes, smaller P. gibbosus individuals will be preyed on by larger wasps. Some birds will even regularly consume wasps. A few examples of birds that prey on P. gibbosus include sparrows, wrens, and summer tanagers. In general, these birds normally exclusively hunt solitary wasps, making P. gibbosus an ideal target. Moreover, the birds avoid disturbing P. gibbosus near their nests.[7]

P. gibbosus has a sting that is painful and menacing enough to deter most potential predators. P. gibbosus's black and yellow coloring serves as a warning to other organisms, as that color pattern often indicates a dangerous species. Additionally, the burrowing behavior of P. gibbosus provides the species with a suitable hiding spot to avoid predators. Because the burrows are so far into the ground, usually around two feet, P. gibbosus is able to avoid predation by remaining in its burrow.[6]

P. gibbosus is most notably parasitized by a nest parasite, Senotainia trilineata, a Miltogrammid fly. P. gibbosus utilizes a flight pattern in which it flies over the nest from above as a means of surveying its nest for the parasite, one that is different from other species of the same genus.[11]

While not much research has been done on which specific pathogens affect P. gibbosus, Streptomyces have been observed to be antibiotic-producing symbionts, which have been suggested to potentially defend their wasp hosts from a variety of pathogenic microbes. This array of phylogenetically diverse and chemically prolific Actinomycetota that has been observed in P. gibbosus suggests that these types of insect-associated Actinomycetota can serve as a source of natural products of pharmaceutical interest for other species.[12]

P. gibbosus is a pollinator of some plants. It has been observed pollinating carrot plants.[13]

P. gibbosus presents a challenge for beekeepers. Because of its tendency to prey on honey-producing bees, P. gibbosus has been known to attack beekeeping sites. This complicates the process of beekeeping and hinders honey production.[14]