Tag Archives: Insects

Do you know how to discriminate male and female houseflies?

A woman walked into the kitchen to find her husband stalking around with a fly swatter.

“What are you doing?” she asked.

“Hunting flies,” he responded.

“Oh. Killing any?” she asked.

“Yep, three males, two females,” he replied.

Intrigued, she asked, “How can you tell?”

“Three were on a beer can, two were on the phone.”

You could amuse your friends and family by telling this joke – or you could amaze them by actually correctly determining the sex of any present houseflies. Read on if you want to learn this “party trick”.

During my PhD study I examined thousands of flies, and counted males and females (I worked on sex determination), so I know what I’m talking about. In the lab, conditions made it an easy job – I could sedate the flies with CO2 and could even use a small microscope to have a better look. But no microscope is necessary if you can get close enough to a fly (or have good eyesight). And if you don’t swat too hard you should be able to distinguish the sex of the corpse. However, I challenge you to determine a fly’s sex when it’s still walking on your table, window or sleeve. It is possible!

Now the most important part – what to look for: you can look a fly between the eyes and/or at the bottom part of its abdomen (the rear part of the body; see the picture below).

Difference between female and male housefly – first column: the head viewed from above; second column – end of the abdomen viewed from below. Figure from Dübendorfer et al. 2002.

The female housefly’s eyes are set further apart than males. Their abdomen is rounder, but pointy at the end and very lightly-coloured when seen from below (lighter that seems on the picture above). On the picture the female’s ovipositor is shown, but it’s usually hidden when she is not laying eggs.

The male’s abdomen is in general slender and has a blunt end. When viewed from below it has a clearly visible dark spot at the end.

And now a small “dry” test before you start your own observations in “the wild”:

Quiz: For each photo determine whether it shows a male or female fly. For the answers see the comment to this post.

The text above concerns the housefly (Musca domestica) – common, blackish fly approximately 7 mm long. I don’t know how to distinguish males from females for all flies (there are 125000 species described), but the eye-distance rule does also apply also to several other flies (e.g. horseflies), and the genitals of many flies look similar. So, using what you learned above for other flies is a good first guess.

Photos: USDAgov – https://www.flickr.com/photos/usdagov/8674435033/sizes/o/in/photostream/, Public Domain, https://commons.wikimedia.org/w/index.php?curid=25727555;  Sanjay Acharya – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=64658576; Judgefloro – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=64830885; Muhammad Mahdi Karim – Eigen werk, GFDL 1.2, https://commons.wikimedia.org/w/index.php?curid=7672794; James Lindsey at Ecology of Commanster, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1970083; Muhammad Mahdi Karim – Own work, GFDL 1.2, https://commons.wikimedia.org/w/index.php?curid=62760319

Did you know that bumblebees find efficient ways to move a ball to a target?

Have you ever watched a bumblebee collecting nectar from flowers? At first sight, this does not seem like a very difficult task, requiring sophisticated cognitive skills.

However, bumblebees have an amazing ability to learn. Not only where to find the nectar, but also how to perform human-designed tricks that require behaviours not needed in nature. For example, bumblebees have learned to pull strings, pull caps aside, and rotate disks to get to a reward.

Not so long ago, scientists (and bumblebees) have taken it a step further. The scientists, in various ways, demonstrated to their subjects that moving a ball into a target (a circle drawn on the experimental platform) led to a reward. The bumblebees quickly learned to do so themselves, and even improved their tactic to be more efficient than those demonstrated.


First, the researchers trained the bumblebees to move a wooden ball, larger than them, to a target – the demonstrator was an artificial insect (on a stick held by the experimenter) pushing the ball. The bumblebees quickly got the idea, but preferred pulling the ball while moving backwards over pushing it. These bumblebees were the demonstrators in the next phase.


In the main experiment, new, untrained bumblebees were divided into three groups. Each insect in the first group could watch another bumblebee dragging one of three available balls to a target and they both received a reward – a drop of sugar water. Insects in the second group saw a ball that moved “by itself” to the target (with help of a researcher-directed magnet under the platform). When the ball reached its destination, the watcher would get a reward. Insects in the third group simply found the ball already at the target with the reward next to it. Each demonstration/trial was conducted only three times.

Then the bumblebees were tested without further demonstration and only got a reward if they brought the ball to the target themselves. Virtually all bumblebees that had had a live demonstrator successfully dragged the ball to the target and did so faster than the other two groups. Those that had seen the ball moving by itself completed about 8 out of 10 trials. Finally, those bumblebees that had simply found the ball next to the reward were successful on average in only 3 or 4 of 10 trials and took the longest.

The student has become the master

Interestingly, the bumblebees did not simply copy what they observed early on. The bumblebee-demonstrator and magnet-using scientist always moved the farthest ball to the target. The student bumblebees usually moved the one closest to the target, even if it had a different colour than the one in the demonstration. And it was not a result of closest ball being pushed accidentally to the target, because the bumblebees usually dragged the ball actually being in-between the ball and the target.

To sum up: firstly, the bumblebees quickly learned a new task requiring the use of a tool (ball) and behaviour that has little to do with normal bumblebee foraging. And secondly, they did not blindly copy a previously observed behaviour, but used a more efficient method – moving the ball closest to the target.

Such unusual experiments show how great a capacity for learning and flexibility in problem solving these common insects have.

Did you know that ants’ brains can grow or shrink depending on their role in the nest?

Indian jumping ant (Harpegnathos saltator)

Many species of ants live in colonies with fixed reproductive roles: one or more queens that lay the eggs, and many sterile workers who forage for food, care for the queen, her young offspring and the nest. In most species these roles are for life, but there’s some in which workers can assume the role of a queen.

One such species is the Indian jumping ant (Harpegnathos saltator). They live in small colonies of about 100 individuals. Colonies are started by a single queen. Most of her offspring becomes workers. When they are young, they work in the nest and their brain is relatively small. Older workers start to forage outside the nest and their brain grows – after all it is needed for spatial orientation, hunting and defence.

When the founding queen grows old, the workers fight to take over her place. The victorious ones turn into so-called gamergates. Their genes related to reproduction activate, hormonal changes occur, egg production begins, and aging slows down. Their behaviour also changes. Experiments have shown that when attacked, the gamergates do not defend themselves, but rather run away. And when they are left alone with a living prey, they do not attack it. Additionally, their brain shrinks (its size is approximately 20% smaller than that of foragers). The work of the brain requires a lot of energy, and since the gamergates are under the constant care of workers, it is better to use this energy to produce eggs than to maintain an expensive organ that is hardly used.

Recently, scientists have shown that all these changes in the gamergates are reversible. When they were separated from the nest for a few weeks and then returned to it, it appeared that they lost their reproductive status. Other ants began to police them so that they would not lay eggs. The former gamergates returned to the role of workers. They stopped producing eggs, spent most of their time outside the nest, began producing venom and started hunting and defending themselves from enemy attacks. Their brain grew back to the size of worker foragers.

Therefore, in this species the brain is very flexible. More so than the brain of bees and fruit flies.

Photo: L. Shyamal – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=64046654

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Did you know that bumblebees give up sleep to care for their siblings?

I still remember months of sleep deprivation after my children were born. In the evenings my husband would take care of them and I would go to bed at eight. Still, I would feel like a zombie in the morning, after waking up every few hours to feed my babies.

If you have children, you probably know what I’m talking about. If you don’t, maybe you will find out one day…

A recent study shows that bumblebees also sleep less when they have offspring to take care of, even though the young are not their own offspring, but siblings. The large earth bumblebee (the species in the study I’m discussing here) is a social insect. In the spring, the queen lays eggs that develop into workers that will take care of their mother and their younger brothers and sisters.

When workers were kept with their younger siblings – in the larvae or pupae stages – they slept much less than if they were kept with a similarly-sized piece of wax (used as a control – so that all the bees had something with them and potentially something to do). And while larvae need feeding, pupae do not. But even pupae need grooming and temperature control – and workers did that. When researchers removed pupae from their cocoon and gave the workers an empty cocoon, at first the workers slept as little as workers with live pupae, but with time they started sleeping as much as the control bees. Most likely pupae release substances that make workers give up sleep in order to tend for the young. When pupae case is empty substances slowly evaporate or degrade.

After the pupae were removed (effect of larval removal was not checked), workers started to sleep more. Where they catching up on sleep? Maybe partially, but researchers speculate that the presence of young modulates the long-term sleep needs of the nurses. That’s because even though workers slept longer after pupae was removed, they still slept less than workers that never had pupae to take care off. If they would be catching up on sleep, they should sleep more.

It’s as of yet not certain whether reduced sleep has just as negative an effect on bumblebees’ performance, cognition or even health as it does on humans. Perhaps like some migrating birds, bumblebees can perform well even under long-term sleep deprivation. If so, I’m jealous!

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