Stump Stabbers

Stump stabbers may look dangerous but these beneficial insects lay their eggs in pests.

Female stump stabber (Bruce Marlin) CC BY-SA 2.5

Like other ichneumon wasps, stump stabbers (Megarhyssa macrurus) help in the fight against garden and landscape pests. Also known as giant ichneumon wasps, their giant stingers are egg-laying organs called ovipositors.


Stump stabber description

Females can be 2” long, reddish-brown with black and orange or white stripes, with an ovipositor that can be 4” long. What looks like a single strand is actually three parts. Two interlocking strands have cutting tips, and a third strand is a tube that transports the eggs to where they need to go. Males are only one-quarter that size and they do not have an ovipositor or a stinger.


Stump stabber behavior

Instead of threatening your picnic lunch, female stump stabbers fly from tree trunk to tree trunk, waving their antennae and running around on the bark. They are listening closely for the sound of pigeon horntail and other wood wasp larvae. Wood wasp larvae chew their way through any decaying wood that may be present in your deciduous trees. Mother stump stabbers use their impressive ovipositors to pierce tree bark and lay their eggs on the pesky larvae. When the eggs hatch, they eat their host and then pupate for the winter.

Pigeon horntail wasp (billmcmillan) CC BY-SA 4.0

You may see male stump stabbers running around and flying around in a similar way, but they are looking for mates, not food.

German stump stabber in action (Frank Vassen) CC BY 2.0

Of course, if you happen to see anything burrowing into your trees, you need to take a closer look. It may be that your tree needs a helping hand.