Big-headed ants (Pheidole megacephala) are not insects with attitude problems, though their invasive behavior, threatening native ant populations, has earned them a place in the top 100 of the World’s Worst invasive species.
The big-head workforce is divided into two groups: major and minor workers. The minor workers are smallish red-brown types. Only the majors, or soldiers (measuring about 3-4 mm), have the disproportionately large heads that give the species its name, though they comprise only about 1% of the foragers. First observed in the island of Mauritius in the Indian Ocean, the ants have spread out to many tropical and subtropical regions of the globe, including Australia and the Americas. They’ve been stirring up trouble in southern Florida for some time now, displacing the native red imported fire ants and white-footed ants. Powerful hurricanes in recent years may have contributed to the big-head problem, when lawns torn up by the wind and rain were repaired with infested sod and vegetation.
Big-headed ants are sometimes confused with termites, as both species create similar “foraging tubes” in the soil; unlike termites, however, the ants don’t have a taste for wood and won’t damage building. Nor are they known to bite unless their nests are disturbed, and their bites are not considered painful.
But they do make pests of themselves in other ways. Foraging expeditions may take them into homeowners’ bathrooms and kitchens, and they produce unsightly “sand piles” on lawns. With numerous colonies that often extend over several residential properties, the little invaders are hard to get rid of.
The large colonies can reproduce year-round, with numerous fertile queens; they sometimes form what’s been described as a “virtually continuous supercolony,” including up to 10,000 ants, that displaces all other insect species in the area. Colonies may be established in the soil and under stones or logs.
The south Florida colonies engage in “nuptial flights” of winged ants in the winter and spring, though “budding” of new colonies have reportedly occurred in Australia without the mating flights. The queens, once impregnated, shed their wings and set up new nesting sites to lay their eggs. They are capable of laying nearly 300 eggs per month.
Incubation time ranges from 13 to 32 days, followed by a larval stage lasting 23 to 29 days and a pupal stage of 10 to 20 or more days. Once fully matured, the minor workers live for some 38 to 78 days (depending on the temperature).
The big-head diet consists of sweet liquids, other insects, and small invertebrates living in the soil. The foragers, frequently marching off in columns, create tunnels with multiple entrances for others to reach established food sources.