Blister Beetles and Bumblebees

In the image above an orange Nemognatha punctulata LeConte feeds on a petal while two Pyrota lineata (striped blister beetles) appear to be mating. The striped beetles are native to Florida and common north of Polk County.

Late summer in Florida, when its too hot and too humid for most annuals to continue producing flowers, cosmos thrive. In my garden the cosmos population is entirely Cosmos sulphureus (orange cosmos). I've tried to introduce other cosmos over the years but only the C. sulphureus survive. These individuals are offspring from years of cultivation. I picked the original seeds from a garden in someone's yard as I was traveling to an appointment a decade ago. The flowers put on such a shocking display I had to stop and pick some of the seeds which quickly sprouted into my own stand of orange cosmos.

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This year, every midday, the cosmos are swarmed with blister beetles and bumble bees. Watching them you can't help but worry about the cute and harmless-looking beetles being so close to the larger and ferocious-looking bees. In reality the beatles are specialized bee predators when they are in their larval stage, and if you watch long enough you'll see beetles clinging to bees hitching a ride back to their hive.

Adult Nemognatha punctulata LeConte, a blister beetle.

This year the flowers are attracting a strange and fascinating array of beetles. These beetles are largely blister beetles (Insecta: Coleoptera: Meloidae). The beetles move around sluggishly compared to the bumble bees that also visit these flowers every afternoon. As they fly in the beetles appear to be in slow motion, like little futuristic flying machines buzzing their way toward the next flower. Once on a flower they defend it while feeding on the flowers orange petals.

This September my garden is full of Nemognatha punctulata LeConte's which are native to the Bahamas, Cayman Islands, and Cuba, but are uncommon north of Dade County Florida. I have thousands in Volusia County, 250 miles north of Miami.

There are 2500 species in the family Meloidae (blister beetles) divided among 120 genera and four subfamilies. The literature claims that Florida is home to 26 of these species. Adult beetles are phytophagous, feeding especially on plants in the families Amaranthaceae, Asteraceae, Fabaceae, and Solanaceae. Most adults eat only floral parts of plants but some can eat leaves as well.

A few of the blister beetles found in Florida are nocturnal, but most are diurnal or show no distinct diel cycle. On my cosmos they are most active mid-day in full sun. Since adults are gregarious and often colorful, they tend to be quite conspicuous. However, larval blister beetles are seldom seen, except for the first instar larvae (triungulins) frequeting flowers or clinging to adult bees.

All blister beetle larvae are specialized predators. Larvae of most genera enter the nests of wild bees, where they consume both immature bees and the provisions of one or more nest cells. The larvae of some Meloinae, including most Epicauta spp., prey on the eggs of acridid grasshoppers. A few larvae prey on the eggs of other blister beetles.

Read more about Florida's species of blister beetles at Ask IFAS: Blister Beetles.

All of the social bumble bee species found in Florida range as far north as Canada. Bumble bees are easily recognized by the corbicula (pollen basket) on the hind tibiae in the females. Honey bees are the only other bees in Florida with this structure, but are easily recognized by their smaller size, hairy eyes, and lack of hind tibial spurs.

Large carpenter bees are often misidentified as bumble bees, but these are readily distinguished from bumble bees primarily due to the absence of pubescence on the dorsum of the carpenter bee abdomen, which is somewhat shiny.

There are a few species of bumblebees that are most common in Florida:

Bombus bimaculatus Cresson 1863, the twospotted bumble bee. Its range extends from Ontario to Maine, south to Florida, and west to Illinois, Kansas, Oklahoma, and Mississippi. Florida county records include Alachua, Clay, Franklin, Highlands, Lake, Levy, Marion, Okaloosa, and Orange.

Bombus fraternus (Smith) 1854, the southern plains bumble bee. Its range extends from New Jersey to Florida, and west to North and South Dakota, Nebraska, Colorado and New Mexico. Florida county records include Alachua, Franklin, Gadsden, Levy, Liberty, Orange, and St. Johns.

Bombus griseocollis (DeGeer) 1773, the brown-belted bumble bee. Its range extends from Quebec and Maine to Florida, and throughout the American West (DL 21011). Florida county records include Alachua, Clay, Collier, Highlands, Marion, and Osceola.

Bombus impatiens Cresson 1863, the common eastern bumble bee. This species is native from Ontario to Maine and south to Florida and was introduced in California and in British Columbia, Canada (EOL 2011). Florida county records include Alachua: Bradford, Calhoun, Escambia, Franklin, Jackson, Gadsden, Highlands, Levy, Liberty, Okaloosa, Orange, Palm Beach, Polk, and Santa Rosa.

Bombus pensylvanicus (DeGeer) 1773, the American bumble bee. Its range extends from Quebec and Ontario, Maryland south to Florida, then west to Minnesota, South Dakota, Nebraska, Colorado, New Mexico, and Mexico (Anonymous 2011). Florida county records include Alachua, Bradford, Collier, Escambia, Flagler, Highlands, Lake, Lee, Levy, Marion, Orange, Putnam, Sarasota, and Santa Rosa.

Bombus terricola Kirby 1837, the yellow-banded bumble bee. Originally, this species extended from Nova Scotia to Florida, west to British Columbia, Montana and South Dakota. While once common, it has declined dramatically since 1990 (Anonymous 2011). No specimens seen from Florida, but recorded from Florida by Mitchell (1962).