Question About Ants Crossing Marker Lines

You’ve probably seen the videos of people drawing circles around an ant and the ant seeming to refuse to cross the line, like this one:

Recently this question came in:

My son wants to do a science project related to a video he saw about ants not crossing a marker boundary. We assume this has to do with pheromones or rather chemicals in the markers. We have tried to find research related to this, however very little has been found by him. Wondering if you know of any research about this?

Before going into the question, first let’s make sure we are clear about terminology. A pheromone is a chemical scent that animals use to communicate with other members of their species. (You can see more about ant pheromones in this previous post.) An ant repellent, on the other hand, is any chemical that keeps ants away. They are not, however, mutually exclusive. It is possible for a pheromone to repel other members of the colony, for example virgin queen honey bees produce a pheromone that tells worker honey bees to back off.

Returning to the marker problem, what could be going on?

It could be the chemicals in the marker act as an ant repellent. The ant is repelled by the line and refuses to cross it. It makes sense that ants respond to any novel or harmful chemicals by backing away or avoiding them.  In a paper in Journal of Chromatography A, scientists found all sorts of chemical compounds in pen ink that ants might want to avoid, including methylbenzene and xylene.

Another possibility that the marker has wiped away the trail pheromone trail that told the ant where to go.

Foraging ants that find food mark the surface with chemicals as they return to the nest. As more ants pass back and forth, more and more pheromone builds up. Depending on the foraging strategies of the ants, some trails can be dense with worker ants. Similarly, when ants are moving from one nest to another, they will lay and follow a pheromone trail.

You can disrupt a pheromone trail with chalk or even with your finger.

The behavior looks pretty similar doesn’t it?

A third possibility is that it is a little bit of both: the marker wipes away the trail and also repels the ant.

Rather than give you all the answers, think about way you might be able to figure out which of the possibilities are likely and how to test for them. A hint: what happens if you draw a pen circle around an insect or spider that doesn’t have a pheromone trail? Do they act the same way?

For more help, check out Drawing Circles Around Ants and Go and Stop? Ant Traffic at the Science Buddies Website. (Always a great resource for science fair project ideas.)

Public domain image of army ants by Alex Wild.

Calling All Ant Bloggers

Do you blog about ants? Know someone else who does? Have a favorite ant-related blog you follow? Please let me know the details or add links in the comments below.

I’m going to be working on a guide to ant blogs over the next week. It will be published on another blog, and the links will be added to the list of websites, forums and blogs page here.

Also, if you are an ant researcher and have some interesting news to share any time throughout the year, let me know and I’ll pass it on to our facebook page.

Thank you!

Formica Pupae: Cocoons or Not?

Tipping over rocks can lead to interesting discoveries.

On a recent trip to western New York, I tipped over a rock.

I found a colony of ants in the Formica fusca group. (They looked silvery, so possibly Formica subsericea, but my eyes are getting older.)

The worker ants scurried to remove the brood to safety.

Something else caught my attention. Do you see it?

Maybe it will be clearer here. Notice the workers are rushing to hide the pupae.

The cocoon on the left is probably a reproductive pupa (queen or male). It is larger than the workers and the cocoon is made of darker, coarser silk.

The cocoons on the right are worker pupae. They are the same size or smaller than the workers and made of lighter silk.

What’s up with the white, naked pupa in the center?

It is the size of a worker. Conventional wisdom says whether or not a larva spins a cocoon before pupating is species specific. Why doesn’t this one have a cocoon like the others?

Some suggestions:

1. Wallis (1960) and others have proposed that Formica fusca larvae must be covered with bits of debris before they can spin a cocoon. Perhaps this one wasn’t buried properly and failed to spin?

2. Perhaps it isn’t a Formica fusca pupa.

Colonies in the Formica fusca group are frequently parasitized or enslaved by other species. This video shows a mixed colony of Formica sanguinea and Formica fusca with a bare pupa.

I didn’t see any evidence of Formica sanguinea workers in the colony I photographed, though.

Have you ever seen Formica pupae without cocoons? If so, why don’t they all have cocoons? What might be the advantages and disadvantages of spinning a cocoon versus not?


I. Wallis, D. (1960). Spinning movements in the larvae of the ant, Formica fusca. Insectes Sociaux. 7: 187-199. 10.1007/BF02224080.

See previous post about Formica fusca group ants.

#amreading Amazing Arachnids by Jillian Cowles

We often see recommendations for summer reads, and although it isn’t lightweight (hardcover at 328 pp), the new book  Amazing Arachnids by Jillian Cowles makes my list.

The American Southwest is full of interesting and unique arachnids. In this book, naturalist and clinical microbiologist Jillian Cowles has captured photographs over over 300 different kinds of arachnids from eleven orders found there, including some that have never been seen before. (The cover photo is by Bruce D. Taubert).

Of course we looked for ants first. They are not listed in the index, but there’s a photograph of a tiny ant mimic spider in the genus Bellota on page 29. Cowles mentions that black widow spiders eat ants (page 200) and has a full page photograph of Euryopis scriptipes spider holding a harvester ant on page 201. On page 245 is a Peckhamia jumping spider that mimics ants and on page 253 there are three genera of ant mimic spiders, Tutelina, Sarinda, and Peckhamia again.

In addition to spiders, the book covers:

  • Scorpions
  • Psuedoscorpions
  • Vinegaroons
  • Short-tailed Whipscorpions
  • Tailless Whipscorpions
  • Microwhipscorpions
  • Harvestmen
  • Wind Spiders
  • Ticks and Mites

Cowles passion comes through in the text. She discusses anatomy and taxonomy for each group before delving into their unusual biological characteristics. For example, she suggests the ability of scorpions to fluoresce at night under UV light may “reflect” a way they protect themselves against the intense daytime solar radiation of the desert Southwest. Cool!

If you are as fond of or fascinated by all things eight legged as Cowles, then Amazing Arachnids is the book for you.

Hardcover: 328 pages
Publisher: Princeton University Press (June 12, 2018)
ISBN-10: 0691176582
ISBN-13: 978-0691176581

Know any children who are interested in spiders? Try one of these two adorable fiction picture books with spider characters.

Disclosures: This book was provided by the publisher for review purposes. I am an affiliate with Amazon so I can provide you with cover images and links to more information about books and products. As you probably are aware, if you click through the highlighted title link and purchase a product, I will receive a very small commission, at no extra cost to you. Any proceeds help defray the costs of hosting and maintaining this website.