The Head of the Bee
After a long day with the bees I’m reminiscing about the time years ago when Bertie Stringer and I were preparing for W.A.S. convention, right on the heels of my visit to Czechoslovakia for the ICOA. I was frustrated with the general public often confusing the yellow jacket for a honey bee. This motivated us to put together a slide show of SEM’s to delve deeply into the differences. These photos are now some of the most interesting of my collections. We’ve been working to add them to our website albums and I thought we could take some time to discuss the head of the bee – a most fascinating thing for me.
In addition to the structures of feeding, the insect head has concentrated sensory structures to perceive the environment it encounters. The bee's head is perpendicular to the ground so mouth parts are more ventral and light and smell structures are more dorsal.
Starting at the top of the head, bees have three separate light sensitive organs called ocelli. Ocelli respond to light intensity and do not form an image.
To the right is a single ocellus up close, surrounded by branching hairs. All bees have branching body hairs and an electrostatic charge. Great for collecting dust particles, i.e. pollen. There is also a pollen grain, or perhaps 3, lying on this ocellus.
Compound eyes on either side of the head extend from the top of the head down about 2/3 of the way towards the mouth. They wrap around the head with most of the eye forward and a bit around the back. The compound eyes are made up of many facets or omatidia, each facing slightly different directions because of the shape of the bee's head. There are roughly 4,000-5,000 facets making up the compound eye of a worker bee. Each ommatidium forms an image and because the shape of the head each ommatidium collects light from a slightly different direction than its neighbors. An overall image is formed by the addition of all the ommatidia but there is some overlap, thus the image is not as clear as the image we see.
The ommatidia are sensitive to color wavelengths of ultraviolet, blue and green (we see blue, green and red). Thus, bees see a trichromatic set of color as do we but the wavelengths are different. Bees can also see polarized light patterns and this enables them to navigate using the sun. They also have an incredible sense of time. We can see this when we watch the bee's dance. They dance in a dark space with no direct sun. A dancing scout bee will change the direction of her dance on the vertical comb to indicate the changing location of the sun over time.
Long unbranched hairs located between the facets of the compound eye give the worker bee information regarding wind speed and direction. Bees know how to explain where the flowers are by dancing on a vertical comb and provide direction, distance, and resource richness. Foraging bees going out must have enough information to get to the flowers, even though the sun will have moved and winds changed.
The long, segmented antennae are movable structures attached to the head, between the compound eyes and below the ocelli. They are covered with many olfactory sensors. Muscles can move them around the plane of the bee's face. Within their base are sense organs, called Johnston's Organ, that tell the bee the direction of movement. The world of the bee is full of odors that tell them many different things...forage, queen, their own colony, and danger are a few. Their antennae (nose) is very sensitive and important for the bee as they live in a world directed by scents.
Below the antennae in this photo to the left we can see some of the mouth parts of the bee. The upper lip, or labrum, is a cover over the preoral cavity. Next are a pair of mandibles, the teeth of an insect. A bee's mandibles are more than teeth: they groom, they mold the wax, they work the propolis, clean cells and more.
The underside of the mandible (to the right) is set with a central row of fine hairs and hairs line the lateral sides. The shape, rounded with smooth outer edge, suggests a spatula with comb teeth.
Combined structures form the lower lip. The maxillae attach behind and laterally to the mandibles. Finally the labium closes the preoral cavity. In the bee the probosis, which we see the bee extend when she sips a droplet of honey from our finger, is a combination of the maxillae and the labium forming the tube through which liquids are drawn.
The tip of the labium (to the left) has a rasping structure allowing the bee to scrape solid sugars, regurgitate liquid onto the scrapings, and suck them up.
What is inside a bees head? Some muscle tissue, nerves that carry messages to and from the brain, mostly olfactory and light sensitive, with some processing cell masses (the brain) and nerves leading from the brain to different parts of the body.
There are glands inside the head as well. Two pairs of glands in the head are responsible for making brood food. One pair are associated with the mandibles and the madibular glands. The other pair are the hypopharygeal or food glands. Salivary, or head glands, are the largest. Another pair, the thoracic glands, lie in the thorax because there is not enough room inside the head. Both pairs connect to the salivary duct.
We hope you've enjoyed this information. Check our website for more SEM's and Tree Hive Bee blogs. Back to the Apiary we go!