Resident bug lover and Project Crimson trustee Ruud Kleinpaste helps us investigate the elusive tiger beetle.
What’s a tiger beetle?
What might it look like? Maybe you want to draw a picture!
Look it up on Google. What does it really look like?
These beetles live as juveniles (larvae – or grubs) in bare clay banks, on the side of tracks through the park or simply on bare soil underneath your feet in the garden.
Look down and you’ll find their distinctive holes in the ground. These are called ‘counter-sunk’ holes.
These holes are the entrances of tunnels (10 to 15 cm long) in which the tiger beetle larvae develop over a year or two. They are very obvious over the summer months, until the larva seals it off and starts forming a pupa (chrysalis) at the bottom of the tunnel.
The adult tiger beetles have long legs and run really fast over the ground, catching flies and other insect prey. They are pretty beetles with patches of iridescent colours on their elytra (wing-covers).
The larvae are also predatory insects, catching small invertebrates (flies, ants, caterpillars) that venture near the tunnels. These grubs have a flat-topped head (with six eyes on the upper surface) that fits beautifully at the top of their tunnel. They can literally block the hole off and look around for 360 degrees as they are waiting for prey.
As soon as you approach the tunnel, the larva will move down and the hole “opens up”. If you stay there very very still, you’ll find that the larvae will crawl back up to re-commence their hunting strategy.
Stick a thin grass stalk into the tiger beetle hole, right down to the bottom and let the stalk sit there. If there is a larva in the tunnel, it will grab the stalk (which makes it move); quickly pull it up and with a bit of luck you may literally be fishing up the larva as it clutches on to your grass stalk.
Look at those predatory mandibles!
How many holes?
- If you have found a whole patch of these tunnels in the soil, see if you can get a mathematical impression of the density of holes per square meter. How would you go about measuring that?
- Can you find another colony of tiger beetle holes somewhere else and make a similar measurement there too?
- Why would the number of holes per square meter be different? Think of plant-cover, light and shade, soil-type, time of the year.
- How fast does an adult tiger beetle run with those long legs?
- With a stop-watch, could you gently shoo it along and measure the time it takes to move a metre along the soil? Some people have clocked it at 5 miles per hour! (how fast is that in centimetres per second?)
What’s in a name?
- Have you heard of a ‘butcher boy’? What about a ‘penny doctor’? Ask your parents!
- Does this species have a name in Te Reo? How can you find out?
- You’ll be surprised to find the following names: hāpuku, kūī, kurikuri, moeone, and muremure.
- Any idea what these names might mean? Have a chat to your koro or tupuna!
- What do you think the hooks on the tiger beetle’s abdomen could be for?