Haploid sons help explain why sisters build empires
Hymenoptera—the sawflies, wasps, bees, and ants—counts over 150,000 living species and more than two thousand extinct ones. Many are parasites; females often wield an ovipositor that doubles as a stinger. Sex is usually set by chromosome number: fertilised eggs become diploid females, unfertilised eggs haploid males.
The Greek name means membrane-wing. Molecular work places Hymenoptera as the earliest-branching holometabolous insects. Fossils begin in the Triassic with Xyelidae; social lineages appear in the Cretaceous. Two pairs of wings typically couple via hamuli hooks on the hind margin. Mouthparts chew, and many species elongate a nectar-sipping proboscis. The ancestral ovipositor sliced plant tissue; most descendants pierce hosts, and in aculeates the tip injects venom while eggs exit at the base.
Symphyta larvae look like caterpillars with thoracic legs and prolegs, but those prolegs lack crochets. Apocrita larvae are legless maggots living inside hosts or nest cells; many cannot defecate until adulthood because the gut is a closed sac. Haplodiploidy gives sisters, on average, higher relatedness than mothers to daughters—one proposed booster of eusociality’s repeated origins. Worker policing—removing other workers’ eggs—follows the same relatedness maths. Haploid males express recessive alleles immediately, purging genetic load; yet diploid males from inbreeding are usually sterile.
Feeding spans leaf-chewing sawflies, predatory stinging wasps that stock immobilised prey, nectar-and-pollen bees, and a vast parasitoid guild. Some are hyperparasitoids of other parasitoids; others steal from galls or nests before killing the occupant. Eggs of the endangered Papilio homerus butterfly have been recorded parasitised at about seventy-seven percent, mainly by hymenopterans. The order splits into waistless Symphyta and narrow-waisted Apocrita. Habitat loss hits hard: as pollinators and parasitoids collapse, plant and pest webs unravel with them. A 2023 ultra-conserved-element study largely confirmed the order’s phylogeny, though basal sawfly relationships remain actively debated.
Source: Hymenoptera
