{"id":12025,"date":"2021-01-27T12:29:08","date_gmt":"2021-01-27T18:29:08","guid":{"rendered":"https:\/\/uwm.edu\/field-station\/?p=12025"},"modified":"2021-01-27T12:29:08","modified_gmt":"2021-01-27T18:29:08","slug":"mexican-grass-carrying-wasp","status":"publish","type":"post","link":"https:\/\/uwm.edu\/field-station\/bug-of-the-week\/mexican-grass-carrying-wasp\/","title":{"rendered":"Mexican Grass-Carrying Wasp"},"content":{"rendered":"

(Note: All links below are to external websites and leave the UWM website.)<\/small><\/p>\n

Howdy, BugFans,<\/p>\n

The BugLady will always associate this wasp with the pandemic. In early summer, she got an email from a BugFan who, because she was working from home (and maybe looking out the window a little bit??), noticed that the track of one her sliding windows had been stuffed with grass. What was going on? The BugLady sent her some info on Grass-carrying wasps and wished that she would see one someday).<\/p>\n

Fast-forward to the Water Hemlock Wildflower Watch (of recent BOTW fame). As she worked her way through the pictures she took on those outings, the BugLady suspected that the fuzzy, little Hymenopteran that she saw was, indeed, a Grass-carrying wasp. Here are some nicer pictures: https:\/\/bugguide.net\/node\/view\/1412306\/bgimage<\/a>, and https:\/\/bugguide.net\/node\/view\/1592431\/bgimag<\/a>e.<\/p>\n

Grass-carrying wasps are, small, benign members of the wasp family Sphecidae, the Thread-waisted wasps (\u201cthread-waisted\u201d because their abdomen is connected to the thorax by a thin stalk called a \u201cpetiole\u201d).\u00a0 Some Sphecids are spectacular in size, shape, and color. https:\/\/bugguide.net\/node\/view\/819298\/bgpage<\/a>, https:\/\/bugguide.net\/node\/view\/1856936\/bgpage<\/a>, https:\/\/bugguide.net\/node\/view\/68796\/bgpage<\/a>, https:\/\/bugguide.net\/node\/view\/1572229\/bgimage<\/a> (All of these wasps have been featured in their own BOTWs).<\/p>\n

Sphecids<\/em> are solitary wasps; most make a nest in the ground that they provision with paralyzed invertebrates for their offspring. The adults are pollinators that sip nectar from flowers (one article said that Sphecids<\/em> prefer white flowers), drink some of the juices of the prey they collect, visit deposits of aphid honeydew, or even take advantage of hummingbird feeders<\/a>.<\/p>\n

Counterintuitively, the Mexican grass-carrying wasp (Isodontia mexicana<\/em>) is the most widespread<\/a> of the six genus members that occur in North America. Bugguide.net lists a pretty reliable (but unofficial) field mark for the MGCW\u2014a brown spot near the base of the petiole, and through the Joys of Photoshop, the BugLady was able to see it on her wasp<\/a>. Besides North America, they\u2019ve also made their way to the UK, to Europe as far east as Crimea, and to Midway Atoll. Not surprising considering their secretive nesting habits.<\/p>\n

They\u2019re found in gardens, grasslands and woodland edges, and when they\u2019re not taking advantage of man-made \u201cbee hotels<\/a>\u201d and window ledges, they nest in crevices and cavities in wood, in hollow plant stems<\/a>, and in tunnels made by other animals (which they clean out before they add their own nest materials). Unlike many Sphecids<\/em>, MGCWs mostly nest above the ground.<\/p>\n

Females gather blades of grass and stuff them into a nest site to form a lining (picture a \u00be\u201d wasp trailing a long piece of grass through the air<\/a>). At the start of the process, she backs down the tube pulling the grass in behind her. When she\u2019s satisfied with the accommodations, she hunts for adult tree crickets https:\/\/bugguide.net\/node\/view\/1163068<\/a>, https:\/\/bugguide.net\/node\/view\/453661\/bgimage<\/a>, and sometimes katydids, which she paralyzes and stows in the nest. She lays an egg near her immobilized prey, and a stalk often contains a series of grass\/tree cricket\/egg units. She finishes by stuffing the entry of her construction with a tuft of grass that some authors describe as \u201cbroom-like.\u201d Curiously, as the sequence of chambers lengthens, the offspring in the later cells (closer to the door) tend to be males.<\/p>\n

There are two generations; the larvae<\/a> of the first generation develop quickly\u2014three to four weeks from egg to adult\u2014emerging in mid-summer. The second generation overwinters as a pupa, in diapause (suspended animation).<\/p>\n

Despite their hiding places, the egg chambers are found by a few species of parasitic fly, and if the fly larva doesn\u2019t kill the wasp larva outright (or starve it by appropriating its food supply), researchers O\u2019Neill, et al found that \u201csharing\u201d its food cache with fly maggots can have a \u201csublethal effect\u201d on the wasp\u2014less food results in a smaller adult wasp that may be less fit.<\/p>\n

Several sources noted that most of the prey in a MGCW nest are adult, female tree crickets, and while this kind of gender bias is uncommon in insects as a whole, it\u2019s common within the Sphecidae<\/em>. Researchers Ercit, Martinez-Novoa, and Gwynne took a look at this prey bias, and here are some of their observations:<\/p>\n