SHARP-EATMAN
NATURE
PHOTOGRAPHY
NESTING BEHAVIOR
of Pickereelweed Longhorn Bees & Their Brood Parasites
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Nesting Behavior
Triepeolus
NESTING BEHAVIOR OF FEMALE MELISSODES APICATUS & TRIEPEOLUS - 2024 & 2025
MELISSODES BEHAVIOR - Preliminary notes
(This is just a general description, briefly summarizing highlights from pages of fieldnotes & Excel sheets, etc.)
In April and early May of 2024 and 2025, female Melissodes apicatus formed a 350-meter aggregation in the fine, white sugar sand of a trail traversing a restored sandhill habitat. Two wetlands with large stands of pickerelweed (Pontederia cordata) lie a mile west and a mile south of the nest site.
Male bee behavior
In 2025, I first saw pickerelweed blooming in Alachua County on April 5. Male Melissodes apicatus appeared on May 8 at the nest site, and were visible by May 6 feeding on pickerelweed at neighboring marshes. Male Melissodes and Triepeolus dominated the nest site through April 17; thereafter their populations decreased until disappearing in the third week of April.
At the nest site, male Melissodes apicatus appeared each day in mid-morning (around 9:30 a.m.), resting on the wiregrass that flanked the trail. After temperatures warmed to about 65 degrees, males would buzz around amid the grass or in the nesting area.
Females also occasionally rested on grass or on dead overwintered plants. Males mated with them either on the sand near nests or on the grass and dead plants. On one morning, I saw a scrum of seven males piling onto a single female resting on a grass blade about 2.5 feet above the ground.
Males were never observed feeding on the scant flora near the nest site. A mile away, at Sweetwater Wetlands, male Melisosdes apicatusfrom unknown locations appeared daily on April 6-17 between 10:30 a.m. and 12:30 p.m. feeding on pickerelweed. They also appeared at La Chua Trailhead (also a mile away), during the same timeframe, nectaring on Florida hedgenettle (Stachys floridana).
Female bee behavior
Female bees emerged three days after males, but did not appear in substantial numbers until mid-April. At the height of nest activity, there were several hundred Melissodes apicatus nests along the sandy trail.
The nesting behavior of the female Melissodes was unusual. The bees’ underground nests lacked visible entrance holes. When the bees entered or left their nests, the sugar sand immediately filled in any surface passageway.
Female Melissodes apicatus, laden with yellow pollen, flew around the nest area, low to the ground, in order to locate their underground nests. They then landed and dug rapidly downward into bare sand until disappearing. The surface sand leveled off behind them, blending in with the surrounding sand and leaving no evidence of the nest entrance.
Females emerged from the entrance points without pollen loads, and covered with brownish-gray dust.
Upon exiting halfway, the bees rotated their bodies, kicking sand around them to fill in any gaps created by their exit. When the bees emerged fully, the surface sand again shifted into place, obscuring the exit path.
The fine dust on emerging bees suggested that their underground nests were built in a substratum where soil consistency permitted tunnel integrity. Soil sampling revealed that a layer of fine, powdery grayish brown dirt enlaced with small rootlets lay under the sugar sand. The dirt increased in moistness and density with depth.
The Melissodes females did not cover or plug nest entrances with pebbles, plant matter or other detritus. They relied entirely on the wide barrier of sand between the surface and their nests below to repel brood parasites and other predators.
The nesting area was visited throughout the day by female Triepeolus (indentified now as T. rugosus). The interactions of this brood parasite with female Melissodes apicatus are shown below.
Temperature & climate
Both male and female Melissodes apicatus showed a preference for a limited range of air temperatures. In early April, the bees emerged in mid-morning, when air temperatures reached 60-65 degrees. The bees then lingered near the nest area, warming themselves by resting on grass strands until air temperatures ranged from 65 to 70 degrees.
In late April, when average daily temperatures climbed toward 80, male bees disappeared from the nest area. In the first two weeks of May, when daily temperatures reached the mid-eighties, the female bee population dropped rapidly, from an estimated 400 active nests, to about 40 active nests. By May 21, only a handful of female Melissodes apicatus remained visible.
Female Triepeolus remained active longer than their hosts. In a one-hour period on April 21, when daily temperatures were in the nineties, I counted 20 female Triepeolus flying low to the ground over the nest area and attempting to enter nests. The Triepeolus avoided sunny areas of the nest site and explored only shady ones -- this may have been a strategy for coping with the heat (intensified by the reflectivity of the white sand). Or, in the alternative, it may be that the only remaining active Melissodes nests were in shady areas where subsurface temperatures were lower.
Floral Associations
As noted in more detail below, Very little flora was in bloom during April and early May in the immediate vicinity of the nest site. Flowering plants became gradually more numerous and diverse as temperatures warmed, but this had no impact on the male or female Melissodes populations.
With the exception of a few bees collected in neighboring parks on Stachys, all of the Melissodes apicatus I observed in Alachua County in spring 2025 were feeding on Pontederia.
Pontederia tends to vanish in the hottest months of the summer in Alachua County and to resurge in the fall as temperatures drop. Given the long bloom period of pickerelweed, and the proclivity of Melissodes apicatus for cool temperatures, it is worth checking whether M. apicatus might be bivoltine here. (I think this is doubtful, but possible.)
Melissodes apicatus males are among the first bee species to appear on pickerelweed in the spring. Females were first observed carrying pollen and feeding on Pontederia cordata a few days after males.
Male Xylocopa micans appear at the same time in large numbers to feed on Pontederia cordata. These are followed, in April, by female Xylocopa micans, female Agapostemon splendens, female Habropoda laboriosa, female and male Xylcopa virginica virginica and female Bombus griseocollis and B. bimaculatus.
In May, as Melissodes apicatus disappeared from the nest site and pickerelweed stands, Florilegus condignus appeared in substantial numbers in neighboring marshes feeding on pickerelweed. Melissodes communis communis also were observed visiting Pontederia in smaller numbers.
During all of April and early May, I observed no Triepeolus feeding on pickerelweed in marshes near the nest site. On May 18, I collected one female Triepeolus (ID pending) on pickerelweed in a marsh 10 miles way.
Insect predators
During the entire period of April 8 to May 6, no insect other then the Melissodes apicatus constructed nests in the sugar sand of the trail occupied by the bee aggregation. Various predatorial insects -- robberflies, beehunter wasps and dragonflies -- occupied the grassy areas flanking the trail, however. Ants established colonies in the grassy area as well, and occasionally intruded individually onto the nest site.
When the Melissodes apicatus aggregation dissipated in mid-May, beehunter wasp and their nests vanished from grassy areas flanking the nest site, and new predatorial species moved in. Among these were antlions, whose nests remained sequestered on the periphery of the nest area as long as the Melissodes were more active.
A female Melissodes apicatus disappearing into its nest
MALES VISITING PICKERELWEED
Pickerelweed flowers grow in spikes, opening from the bottom up. They began blooming this year in Gainesville in the first week of April.
These photos show male Melissodes apicatus on April 6-7, 2025, drinking nectar from pickerelweed at Sweetwater Wetlands. Females did not emerge until a week later.
Male pickerelweed longhorn bees were among the first bee species to appear on the flowers.
NEST HABITAT
The 2025 nest aggregation stretched for 350 meters along a sugar sand trail in a restored sandhill habitat.
On either side of the trail are swaths of wiregrass (Aristida stricta) that are 10 to 40 meters wide. On the far edges of the grassy clearings are longleaf pine trees, and sporadic saw palmetto, cabbage palm and live oak.
The wiregrass grows sparsely along the trail, in well-spaced bunches.
& BEES RESTING ON GRASS & MATING ON SAND
At the 2025 Gainesville nest site, male bees spent most of their time in the grassy borders flanking the trail. They did not feed in this area, which in April contains few flowering plants.
In April, the clumps of wiregrass (Aristida stricta) flanking the trail were 2/3 to 1.5 meters high and widely spaced.
Around 10:00 a.m. on cool mornings, individual male bees appeared resting on grass blades -- possibly to warm themselves. This photo shows one of 40+ males doing this on a single morning. Similar photos follow.
NEST BEHAVIOR OF MELISSODES FEMALES
A Melissodes apicatus flying over the trail to locate her nest.
This is a Melissodes female excavating its nest entry portal after returning from collecting pollen.
The yellow pickerelweed pollen on the bee's legs is dense and gluey; no pollen falls off as the bee digs vigorously into the ground.
INSECT PREDATORS VISITING NEST SITE
Various predatory insects established themselves in the open grassy areas flanking the trail. None of these built directly in the sugar sand trail dominated by the Melissodes nest aggregation.
The nests of beehunters (Philanthus sanbornii) were especially numerous: within five meters of a small cluster of 10 Melissodes apicatus nests, I counted 15 beehunter nests.
Lateral view of a Philanthus sanbornii. (In Florida, this species is redder than its northern counterparts.)
BEE-ANT INTERACTIONS
In late April, individual Florida harvester ants (Pogonomyrmex badius) appeared amid the Melissodes aggregations to carry away dead bees (possibly as an act of necrophoresis).
Here, a Florida harvester ant begins to drag the eviscerated carcass of a female Melissodes apicatus. The ant's nest lay several meters from the Melissodes nest site.
Sometimes, when scavenging for dead bees, ants approached Melissodes apicatus females half buried in sand as they descended to their nests. The ants would prod the bees, as if testing them to see if they were alive. The bees used their hind legs to push away the ants, which would then depart.
TRIEPEOLUS BEHAVIOR - Preliminary notes
Emergence dates
In 2025, male Triepeolus emerged at the nest site on April 8. Males mated with females on the sandy trail of the nest area and disappeared by the third week of April. Female Triepeolus remained flying through the second week of May.
Female Triepeolus behavior in nest area
Brood parasites such as Triepeolus often locate ground nests fairly easily by searching for entrance holes to underground tunnels. The Melissodes apicatus aggregation, however, proved unusually challenging to its brood parasites, because the nests lacked entrance portals.
Female Triepeolus were unable to pinpoint nest locations without first observing a female host enter the sand. Thus, despite the fact that the nest aggregation counted several hundred nests at its height, most of the female Triepeolus' time and activities focused on simply finding the nests.
Female Triepeolus patrolled the nest site from around 9:30 a.m. through noon each day, flying low to the ground in search of nest activity. Occasionally, a female Triepeolus would drop to the ground to search for nest entrances and commence digging here and there in the ground. The bee might dig so deeply that it submerged the front half of its body in the sand -- only to withdraw a few minutes later, having failed to find a nest entry portal.
More commonly, Triepeolus females would wait for the arrival of a female Melissodes returning from a marsh, its legs laden with pollen. When a Melissodes alighted in the nest area, a female Triepeolus would perch nearby (roughly 30-45 cm away), on the bare sand or a piece of plant detritus, watching as the Melissodes swiftly located its nest entrance, dug into the sand and disappeared.
The Triepeolus would then wait for the host bee to emerge -- in some cases, the female pickerelweed longhorn would emerge in 15 minutes, but in others hours would pass without the host bee resurfacing. A waiting Triepeolus was sometimes joined by other Triepeolus piggybacking on its discovery.
If the host bee failed to resurface within half an hour, the attendant Triepeolus usually abandoned their vigil. No Triepeolus was ever observed entering a nest portal while the host was still inside.
If a Melissodes resurfaced soon after entering, the waiting Triepeolus would rush toward the host and stand a few centimeters from its exit point as it quickly emerged. Sometimes the host bee would have to push the Triepeolus away while still exiting the sand. Other Triepeolus observing the commotion might then charge toward it to capitalize on the discovery of the exit location. The newcomers would vie with the Triepeolus already there, jostling to enter the nest first.
As soon as a host bee departed, any waiting Triepeolus would dig into the sand at the exit point -- much more slowly and less efficiently than the Melissodes. A typical Melissodes apicatus could disappear into the ground in sixty seconds, but the Triepeolus labored as long as five minutes before disappearing into the passageway of sand loosened by the upward journey of the host. After succeeding in entering the underground nest, the Triepeolus female would remain hidden for five to ten minutes before reappearing.
If two or more Triepeolus vied to dig into the entryway simultaneously, one victor usually emerged, and a single bee would make the descent into the nest. Less often, two bees would dig at once; this sometimes resulted in the entrance location being lost in the rivalry, and neither bee would find the correct entrance point.
Floral associations:
No female or male Triepeolus were found feeding on plants in the vicinity of the nest site. Nor were any Triepeolus resembling those at the nest site found on pickerelweed in neighboring marshes.
Difficulties in identifying nectar sources for the Gainesville Triepeolus stemmed from the nest site's location in an area where few plants bloomed between March and early May.
During April, the predominant flowering plant was spurge nettle (Cnidoscolus stimulosus). Slimleaf pawpaw (Asimina angustifolia) blossomed along the trail in late April and early May. Neither of these plants, however, attracted bees. Other flora found in limited quantities during April included frostweed (Crocanthemum corymbosum & C. georgianum), low prickly pear (Opuntia humifusa) and, in the third week of April, a stand of blackberries (Rubus cuneifolius) set back 30 meters from the trail where the Melissodes aggregation was situated.
From April 1 - May 5, no bees of any species were found feeding within 50 meters of the nest site, with the exception of three Lithurgopsis gibbosa on prickly pear. This was despite weekly inventories of plants and searches for bee species feeding on flora.
Neither Mitchell (1963) nor Rightmyer (2008) noted floral records for Triepeolus georgicus. Hall & Ascher reported finding Triepeolus georgicus on Asterceae in sandhill habitats -- specifically, one female on bushy aster (Symphotrichum dumosus), and one male on slender goldentop (Euthamia caroliniana), at Kanapaha Prairie, located 13 miles from Sweetwater Preserve; and one male on coastal plain honeycombhead (Balduina angustifolia) at Ordway-Swisher Biological station. (Hall & Ascher 2014: p. 9, table 3; Hall & Ascher 2010: p. 662, table 3).
A female Triepeolus exploring a nest exit location after the Melissodes apicatus host has departed
A female Triepeolus beginning its entry into the sand
A female Triepeolus digging into the host's exit location
After watching patiently for the host Melissodes to depart the nest, a female Triepeolus approaches the location where the longhorn bee exited.
The Triepeolus digs to find the sandy passageway from which the host emerged.
The Triepeolus dives headfirst into the soil.
This is the nest site of a Melissodes apicatus. The sand surface reveals no trace of an entryway to the nest.
When the female Melissodes below swims upward through the sand from her underground nest, the surface sand quivers, and a faint depressed circle appears at the entry point.
In response to movement in the sand, a Triepeolus stations itself near a possible nest hole. This Triepeolus has been waiting next to the nest for 30 minutes, after watching a female enter laden with pollen.
At the 2024 nest site, a female Triepeolus hovers over the trail, watching for Melissodes activity.
The Triepeolus lingers nearby as a Melissodes disappears into its nest.
The Triepeolus remains after the Melissodes apicatus female disappears.
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