Bug o’the Week
by Kate Redmond

Birch Catkin Bug

Howdy BugFans,

When the BugLady started this little project in the summer of “twenty ‘aught seven,” she had two criteria for candidates for the bug of the week – that she had taken a decent picture of the bug, and that she was able to find an interesting story about it.  Today’s episode sets the bar pretty low for picture quality.

This adventure started with a (very) bad photograph.  Last week, the BugLady headed to a little bog that she frequents so she could test drive her new macro lens.  She photographed the spiffy male catkins of an alder, and then she aimed the camera overhead at a cluster of last year’s female cones, just to see what the lens would pick up.  A “throwaway shot.”  When she put the picture up on the screen that evening she realized that the camera had seen a bunch of small bugs that she had not, and although she massaged the image, it was still pretty sad.  So she went back the next day – with much the same result.  That’s how it goes, sometimes, but here are some splendid pictures of the bug: https://www.britishbugs.org.uk/heteroptera/Lygaeidae/kleidocerys_resedae.html.

The first thing she noticed on Trip #2 is that although she checked the cones on alders all along the boardwalk, she only saw the bugs on alders that grew fairly close to the shoreline of a small, adjoining lake.  The second thing she noticed is that these bugs are slippery little devils – when she gently hooked the branch of a tall alder to bring the cones down to camera level, the bugs had vanished by the time the cones got close.  The third thing she noticed is that this was a bug that she’d never seen before (a “True bug” in the Order Hemiptera, and the suborder Heteroptera, because of the “X” arrangement of the folded wings on the back). 

Brief, slightly technical digression (but it’s spring, but our brains are yawning and stretching and greening up, and we’re up for this):  Once upon a time, there was an insect order called Homoptera, which included cicadas, leafhoppers, spit bugs, scale insects, aphids, and the like.  A separate order, Hemiptera, was called the “True Bugs,” and it included stink bugs, leaf-footed bugs, assassin bugs, seed bugs, etc. – the guys with the X’s on their backs.  The two Orders were merged, under the umbrella of “Hemiptera,” and the true bugs are now in a suborder called Heteroptera (which means “different wings,” because their front pair of wings is leathery at the base and membranous at the tip).

BIRCH CATKIN BUGS (Kleidocerys resedae) are in the suborder Heteroptera and in the Seed Bug family Lygaeidae – “Seed bugs” because most family members (like Milkweed bugs) feed on seeds, puncturing them with piercing mouthparts.  Due to the chemicals they pick up from the plants they eat, many Lygaeids don’t taste so good, and some (like Milkweed bugs) are clad in bright colors to advertise that fact.  Most Lygaeid species also have stink glands, and so the term “stink bug” may be applied pretty loosely, but the Hemipterans that are officially called Stink bugs belong to the Stink bug family Pentatomidae.  Birch catkin bugs have an odor that some people call strong and unpleasant, but that blogger Larry Hodgson, the Laidback Gardener, described as “intense, with a hint of wintergreen.”

The BugLady was surprised to learn that this little bug’s range is Holarctic, a term that refers to much of the Northern Hemisphere, around the globe.  It didn’t come over on the boat – it’s native to northern portions of both the Old World (the Palearctic) and the New (the Nearctic) https://bugguide.net/node/view/100506/data, and it’s never far away from its host plants in the genus Betula – the birches.  The BugLady found some good information about it on nature sites in the United Kingdom. 

If you figure that a mature alder cone is about two-thirds of an inch long, you can see that these are very small insects, indeed – maybe 3/16” long, max.  They are generally rusty-colored, with clavate (clubbed) antennae, and they’re “densely punctate” – covered with small pits or punctures https://bugguide.net/node/view/1598589/bgimagehttps://bugguide.net/node/view/1440751/bgimage https://bugguide.net/node/view/524365/bgimage https://bugguide.net/node/view/168566/bgimage    

Birch catkin bugs eat birch seeds, which are found in the female catkins/cones.  Although the nymphs have a strong attachment to their birch host plants, adults do use other trees and shrubs, like the Ericaceae (heathers and blueberries) and the Rhododendrons; bugguide.net lists “alder, and other deciduous trees/shrubs” among the adult food plants.  The BugLady guesses that the bugs she saw were looking around for any of last-year’s seeds that may have weathered the winter within the cones, since the new alder cones won’t be producing seeds for a while.

They overwinter as adults, sheltering in old, fallen catkins and in leaf litter (though in some areas where there are several generations per year, nymphs may also overwinter).  They wake in spring and mate in June, and according to several sites from the United Kingdom, “whikst [sic] flying they emit a vocal mating calls using a strigil [a comb-like scraper] located on one of the hind wing veins.”  Females lay eggs on old, female birch cones. 

THE RABBIT HOLE DU JOUR: The BugLady was curious about the statement about Birch catkin bugs emitting mating calls in flight.  Rubbing two body parts together to produce sound is called stridulation, and it isn’t uncommon – think locusts and katydids – but it’s not universal, either.  Milkweed beetles stridulate, and Hemipterans like tree hoppers do, too, and depending on the species, adults, larvae, and even pupae may stridulate.  Here’s what she learned from a wonderful (and very scholarly) paper in Biological Reviews called Sexual selection and predation drive the repeated evolution of stridulation in Heteroptera and other arthropods, by L. Davranoglou, G. Taylor, and B. Mortimer.  

  • Kleidocerys makes noise by striking a file on the wing against a scraper on the thorax (Another reference said that both male and female Kleidocerys “sing,” and they produce the same song).
  • The main ways arthropods generate vibroacoustic signals is by stridulation.
  • Stridulation is often used by species that live in/on soil, leaf litter, plants, and water.
  • Stridulation seems most often to be associated with defense and with courtship/mating (or with a combination of the two). 
  • The body parts that are used as stridulatory organs are often those used in grooming, and grooming is a common part of courtship and mating rituals.
  • BUT (emphasis, the BugLady) – most Heteroptera don’t have tympanal organs (“ears”)!  When they make sound, they can’t hear it – at least not as we define hearing – but can probably perceive/”feel” it as vibrations through the substrate, the surface they’re living on.  If the stridulation is defensive, then their predators can probably hear it. 
  • As a group, aquatic bugs like water boatmen, giant water bugs, backswimmers, water scorpions, etc., do have tympanal organs (and some have tympanal organs but they don’t stridulate, a story for another day). 

Cool paper.

Are they pests?  Since they mainly feed on the seeds, there may be a very slight cosmetic impact if catkins turn brown, but few of us plant birch trees for the seeds.  There were several accounts of big infestations where Birch catkin bugs ran out of catkins and nibbled on birch leaves late in the season and marched across the landscape (with a few accidentally coming inside homes, where there’s nothing for them to eat, so they die) (crushing the intruders is not advised).  They are said to gather on warm, exterior walls on fall days, like box elder bugs, but even though some accounts list them as “common,” most people (like the BugLady) have never noticed them.  The Minnesota Seasons website says that “Based on the number of reported sightings, it is relatively uncommon in Minnesota. However, it is probably under-reported due to its small size.” 

Go outside – find a wetland!

Kate Redmond, The BugLady

P.S.  THEY’RE COMING!  The BugLady loves interactive maps.  Be sure to set the map for 2023: https://maps.journeynorth.org/map/?year=2019&map=monarch-adult-first.

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