#33: Hamuli

A row of hamuli on the wing of a bee

The top two hamuli shown here are hooked onto the
back edge of the forewing.

Litinsects #33: Hamuli

Today’s post is another on anatomy and is about a structure found in a group of insects that probably everyone around the world is familiar with...

The order HYMENOPTERA is comprised of bees, wasps, sawflies, and ants. (Yes, ants are actually related to bees and wasps.) At around 150,000 described species it is among the top 4 largest group of insects (along with beetles, flies, and butterflies).

One defining characteristic of hymenopterans are HAMULI (see photos). Hamuli (singular hamulus) are microscopic hook-like structures on the front surface of the rear wing that hook into the back edge of the front wing. This system interlocks the two wing pairs during flight, allowing them to beat in unison and act as one functional pair of wings. Basically hymenopterans have developed an anatomical wing coupling feature to enhance flight efficiency. (In the third photo you can see the top two hamuli hooked into the fore wing!)

The reason I wanted to explain hamuli is because there is a cool tie-in as to why this group is named hymenoptera. Two explanations exist for the etymology of the word; we already know the second part of the word refers to the wings, but what about the first part?

(1) “Membrane-winged”: The Greek word “hymen” means membrane, which makes sense since they have relatively few wing veins compared to other groups.

(2) “Married wings”: Now that we know what hamuli are, the second explanation makes sense as well: Hymeno is the Greek god of marriage so the name might also be a reference to the fact that the wings are “joined together” in flight.

While we’re on the subject, I wanted to share another cool feature of the group: the system of sex-determination, known as HAPLODIPLOIDY. In hymenopterans, sex of offspring is determined by how many sets of chromosomes they have. Unfertilized eggs contain only 1 set (the chromosomes from the mother) and develop into males, while fertilized eggs contain 2 sets (one from each parent) and develop into females. What is quite interesting is that egg-laying mothers actually have control over the sex ratios of their offspring. As an egg is laid, a muscular ring at the end of the sperm duct controls whether a sperm is let through or not.