Having hijacked some part of a plant’s tissue, gall-makers cause it to form not just a lump, but a very specifically-shaped lump.  In the usual MO, the gall-maker exposes a small area of a growing stem/petiole/leaf/bud/flower to a chemical that acts like a plant growth hormone and signals the plant to grow extra tissue in that spot, either as extra cells or as extra-large cells.  In some cases, the chemical is introduced by Mom when she oviposits.  In the case of animal-induced galls, the extra tissue grows around the mite, nymph, or larva, providing it with a climate-controlled, relatively (but not infallibly) predator-free shelter whose walls are edible. 

The lives of some gall-makers are simple, and the lives of others are more complex, and today, we have one of each.  One is an aphid, and one an aphid relative called an adelgid, both in the bug order Hemiptera.  There are some physical differences between aphids and adelgids, but reproductively, adelgids always lay eggs, and aphids may go many generations giving birth parthenogenetically (female aphids popping out more female aphids without eggs or the input of males) before producing a generation that includes males.  No male Norway spruce gall adelgids have been observed.   

The BugLady didn’t have to go far to find a NORWAY SPRUCE GALL/EASTERN SPRUCE GALL/PINEAPPLE GALL – she looked over as she was hanging a hummingbird feeder in a Norway spruce and thought – hmmm (as Isaac Asimov once said, “The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ (I found it) but ‘That’s funny…”  They’re formed by the Eastern spruce gall adelgid (Adelges abietis), family Adelgidae https://bugguide.net/node/view/587480/bgpage.   

Norway spruce gall adelgids are not native, having immigrated from Europe to Canada more than 125 years ago.  They are now found throughout northeastern North America and in Appalachia as far south as Tennessee, plus a few western locations.  Various species of spruce are their only hosts.

They have a one-year life cycle (most adelgids have a two-year cycle).  Tiny Norway spruce gall adelgid nymphs (“sistentes”) overwinter at the base of the needles (their name when they’re overwintering is “neosistens”).  In spring, these become “stem mothers” (“fudatrices”) that lay eggs on needles at bud break.  In 10 days, the newly-hatched nymphs start eating the needles, and their saliva causes a gall to form that houses about a dozen nymphs, each in its own chamber https://bugguide.net/node/view/483860/bgimage. 

In late summer, when the galls dry and open, the nymphs emerge and molt into winged females https://bugguide.net/node/view/587480/bgimage that disperse (but not very far – they’re pretty weak flyers), feed, and lay eggs.  According to the narrative on one bugguide picture, females die after laying eggs but shelter the eggs with their bodies https://bugguide.net/node/view/587481.  These eggs hatch in fall and the nymphs overwinter at the bases of buds, poised for the spring.  Here are some life cycle pictures https://bugguide.net/node/view/587476/bgimage.  Old, empty galls resemble pine cones. 

If you have Norway spruce galls, do you need to do anything about them (other than admire them)?  They don’t spread very fast (and some individual trees have a resistance to them), and they don’t prevent shoots from growing, though some exterminator sites warn that they can reduce the vitality of the tree, and the extra weight may cause branches to break.  And Christmas tree farmers don’t love them.

ELM COCKSCOMB GALLS are made by Elm cockscomb gall aphids (Colopha ulmicola) https://bugguide.net/node/view/539171/bgimage, family Aphididae (ulmicola means “elm dweller”).  The galls are described as tubular and “wormlike,” starting out green and turning red (like a cockscomb https://bugguide.net/node/view/1373502/bgimage) as summer progresses, and ending up brown.  If Norway spruce galls are camouflaged, these elm galls sit in plain sight on the surface of a leaf, with several sometimes growing on one leaf https://bugguide.net/node/view/1936031/bgimage.   

They’re found on American and red/slippery elms in an odd, patchwork distribution https://bugguide.net/node/view/223263/data.

Unlike the Norway spruce gall adelgids, the aphids don’t spend their entire lives in the same place.  During the summer, the aphids live underground, sucking juices from grass roots.  They emerge in fall to produce a winged generation of males and females that mate, after which the females hide a single egg in elm bark (one source said that the eggs are laid between bud scales).  As the new elm leaves start to grow in spring, the tiny, newly-hatched aphid nymph finds them, starts feeding, and stimulates the growth of the gall.  When she (all of the aphids in this generation are females) matures, she becomes a stem mother and starts cranking out hundreds of young, sans eggs, still within the gall, all feeding and producing honeydew.  In early summer this generation, which is winged, exits through a slit in the underside of the leaf and heads down to feed on grass roots. 

Here are some pictures of the life stages https://bugguide.net/node/view/1936031/bgimage.

Michael J. Raupp, Professor of Entomology, Extension Specialist at the University of Maryland Extension, writes the excellent (and original) Bug of the Week.  His article about the Elm cockscomb aphids includes a video of the aphids dispersing as well as this description, “On bright autumn afternoons the air near my elm is filled with a flurry of elm cockscomb gall aphids returning to their winter home, which is a Princeton elm. Watch as a female alights on an elm branch briefly before taking off, perhaps in search of another place to lay eggs or to escape my camera lens. For a much closer look, check out the aphid through the lens of a microscope. These are pretty cool insects.”  https://bugoftheweek.com/blog/2022/10/15/sunny-with-a-chance-of-aphid-flurries-elm-cockscomb-gall-aphid-colopha-ulmicola

Other than being unsightly/fascinating, they typically cause no damage to the tree. 

Galls!

Kate Redmond, The BugLady

Bug of the Week archives:
http://uwm.edu/field-station/category/bug-of-the-week/