Macrotera portalis facts for kids

Quick facts for kids Macrotera portalis
Face of a large-headed, flightless male of Macrotera portalis. This bee was marked with yellow paint for studies.
Scientific classification
Synonyms
Perdita portalis Timberlake, 1954

The Macrotera portalis is a fascinating type of bee that lives in groups and builds its nests in the ground. These bees are found in the dry grasslands and desert areas of North America. They are specialist bees, meaning they only collect pollen from one specific type of plant: the Sphaeralcea, also known as globe mallows. These clever bees time their appearance to match the desert's monsoon rains, helping them survive the tough conditions. They can also have two or even three generations of young bees in a single year.

The Macrotera Portalis Family Tree

The Macrotera portalis bee belongs to the insect order Hymenoptera, which includes bees, wasps, and ants. It is part of the family Andrenidae, often called mining bees, and its specific group is the genus Macrotera.

This species used to be in a much larger group called Perdita. That group still has about 600 species of bees, mostly found in northern Mexico and the dry southwestern United States. However, about 30 species, including Macrotera portalis, were moved from Perdita into the Macrotera genus.

What Does a Macrotera Portalis Bee Look Like?

Macrotera portalis is a small, dark bee, usually about 7 millimeters long. Like most mining bees, it has small grooves or dimples on its face, located between its eyes and where its antennae begin. These are called facial foveae.

One very interesting thing about M. portalis is that its males come in two different forms or sizes. This is called dimorphism.

This bee is closely related to another species, Macrotera texana. Both types of bees live in groups, and the females prepare more than one cell for their young each day. It's also common for bees to find partners within their nest. However, Macrotera portalis nests usually have more females, and these nests are often used again for many years. In contrast, M. texana males are not dimorphic, and their nests are usually not reused for several generations.

Where Do These Bees Live?

You can find Macrotera portalis in the dry grasslands and desert regions of northern Mexico, Arizona, and New Mexico.

How Macrotera Portalis Bees Build Their Homes

Like other bees in the Andrenidae family, M. portalis bees dig their nests in the ground. They are also communal, meaning many female bees often share the same main nest. However, each female builds and cares for her own separate little room, called a "brood cell."

These brood cells are small side chambers off the main tunnel. Inside each cell, the female places a food ball made of pollen and nectar. She then lays a single egg onto this food ball before sealing the cell. A baby bee, called a larva, then grows inside. The females are very picky eaters for their young; they only gather pollen from globe mallow plants.

Typically, there are between 2 and 29 adult females living in one nest. Each female is responsible for building her own cells. In these shared nests, each female usually makes one cell per evening. There's no sign that they help each other build. If two or more females share a side tunnel, they each seem to keep their part of the tunnel in good shape. They don't seem to cooperate or fight over the tunnels. All the females help keep the main tunnels and side paths clear by pushing soil into the walls.

The nests are not very deep, usually less than 15 centimeters. However, some complex nests can have over 200 cells in an underground area about 20 centimeters wide. The main tunnels go straight down and are not lined, but the brood cells are horizontal and have a special waterproof lining. The nests stay open during the nesting season and don't have mounds of dirt outside the entrance unless new cells are being built. Females dig new tunnels or cells using their jaws to loosen soil. They push the soil backward with their legs into an open side tunnel. Then, they clear the loose soil by walking backward and using their legs and abdomen to push it into a nearby tunnel.

Females usually follow a daily routine: building a cell, filling it with food, laying an egg, and then closing the cell. Females who have been out foraging return and shape loose pollen into a sphere, creating a pollen ball. If a male is present, the female might pair up with him as she leaves the nest. After an egg is laid and the cell is closed, the female leaves the nest for a feeding trip, but she doesn't bring back any pollen. Cell construction involves shaping the cells by repeatedly packing the soil using a special plate on the female's rear, adding more soil when needed. Once the chamber is smooth and packed, a waterproof lining is added. The female brushes her abdomen over the cell to create this lining. Females do not open cells after laying an egg or check if other insects have stolen their food or young.

Even though many bees live together, they don't seem to guard the nest entrance. Scientists think that living communally is most likely because building a nest alone would be too much work for one bee.

Who Are Their Enemies?

M. portalis bees face threats from other insects. Blister beetle larvae have been found in their nests, digging tunnels between cells and eating the young bees. Nests can also be attacked by fire ants called Solenopsis molesta, which take the bee pupae (the stage before adulthood) as food. Velvet ants (Mutillidae) in the genus Pseudomethoca, like Pseudomethoca perditrix and Pseudomethoca toumeyi, are also parasites. They attack the bee pupae in the nests, but leave other young bees alone.

The Life Cycle of Macrotera Portalis

Macrotera portalis bees can have two, or sometimes even three, generations of young bees each year. This means some young bees grow up and appear as adults in the same year their mothers did. The journey from a larva to an adult takes at least 21 days.

Adult males and females usually come out of their cells in spring or summer. They then find partners to have young. Females lay eggs and continue to prepare and build brood cells while the young bees develop. Some males stay in the nests.

During winter months, the young bees (larvae) go into a resting state called diapause. They stay in this state as pre-pupae or almost-adults. Diapause continues until the next spring or summer monsoon rains arrive. Then, some of them wake up and become adults. Some young bees can even stay in diapause for over a year!

Smart Survival Strategies: Bet Hedging

Bet hedging is a clever strategy where animals try to make sure some of their young survive, even if conditions are bad in certain years. Macrotera portalis uses bet hedging because only a certain number of bees emerge in any given year, with many remaining in diapause. This means that not all young bees come out at once. Even if fewer young appear in one year, it helps ensure that some will survive if resources are scarce. This strategy helps the bees deal with unpredictable desert life, where conditions can change a lot from year to year.

Desert bees that spend the winter underground have a short time to be active and have young after the rainy season. Young bees face many dangers: high heat, dry air, being buried in the soil, predators, drying out, and diseases.

Their emergence is often triggered by rainfall, especially the late summer monsoon rains in the southwestern desert. This means many bees appear at the same time. Scientists have noticed that slightly more large-headed males tend to appear before small-headed males. When comparing young bees that emerged in the same year they were born to those that waited an extra year in diapause, the ones that emerged sooner were much lighter. This suggests that if a young bee has enough stored energy, it will wait longer in diapause. Lighter bees, with less energy, tend to emerge sooner. These lighter bees are also found deeper in the soil than those in diapause. So, emergence is influenced by the young bee's condition and also by rainfall.

Bee Families in the Nest

Nests are often used again by many generations of bees. This means the bees living in one nest are usually like a big family, closely related to each other.

Different Kinds of Males: Dimorphism

Having two different types of males, called dimorphism, is a special feature of this bee species. The two types are different in their shape and head size:

• Small-headed males can fly. After they appear, these males are often found on flowers. They can be quite competitive, sometimes fighting with other males of their own species or even with other types of bees. Small-headed males often pair up with females who are out collecting food.

• Large-headed males cannot fly. They have special features like weak flight muscles, bigger facial grooves, and smaller eyes. After they appear, these males stay inside the nests with the females. Large-headed males are also very competitive. They can have intense fights using their jaws, and sometimes one male might not survive. Large-headed males pay close attention to the females' activities. They stay near open cells when females are preparing them and pair up with females when they are making food balls for their young, just before laying an egg.

How Many Males and Females?

In one study, out of 167 young bees, about 45% were female and 55% were male, which is very close to an equal number of each. Among the males, there was also an almost equal number of large-headed and small-headed males (about 52.5% large-headed and 47.5% small-headed).

Finding a Partner: Reproduction Roles

Smaller-headed males usually find partners outside the nest, while the large-headed, flightless males find partners inside the nest. So, their head size is connected to their strategy for having young. Large-headed males might compete more directly, while small-headed males might use a "sneakier" approach to find partners. Both strategies help them pass on their genes.

The food a young bee eats affects its size. This means a mother bee, by how she feeds her young, can influence what kind of male her offspring will become. Scientists think that the larger males' competitive strategy might be more successful on average, but more research is needed to confirm this.

Specialist bees like Macrotera portalis often gather in places where there are lots of resources, like flowers. Both types of males have ways of finding partners. Large-headed males stay in the nests where females emerge, while small-headed males gather at places with lots of flowers. These strategies make sense because females are found in both these areas.

Protecting Macrotera Portalis

Currently, there is no specific information about the conservation status of this bee species.