#cynipidae

Above: plant growths caused by the larvae of three different species of gall wasp, including Trigonaspis teres, Callirhytis seminator, and Feron izabellae

These tumor-like growths are known as plant galls. They develop in response to chemicals that are injected or secreted by certain insects, mites, and nematodes. Each plant gall forms around the body of a single larva (or, in some cases, a small group of larvae), and the structure serves as both protection and sustenance for the tiny creature developing within.

Above: the plant gall of the oak apple gall wasp, Atrusca quercuscentricola, with a bisected view that shows the larva within

There are many different insects that can trigger the production of plant galls, including certain aphids, psyllids, flies, beetles, scale insects, and caterpillars, but gall-forming wasps are especially diverse. They also create some of the most distinctive plant galls in nature.

Above: the photo at the top shows the plant gall of an unidentified gall wasp from the family Cynipidae, and the photo at the bottom depicts the plant galls of the urchin gall wasp, Cynips quercusechinus

The color, shape, size, and texture of each plant gall varies depending on the species of gall wasp that induces it. Some wasps are associated with plant galls that look like fuzzy little pom-poms; others produce mushroom-shaped structures, colorful discs, cones, pink spheres, cottonballs, etc.

Above: this photo shows a mushroom gall wasp, Heteroecus sanctaeclarae, which produces plant galls that look like tiny mushroom-shaped houses

As this article explains:

Galls are plant growths (similar to tumors) that are induced by various organisms such as bacteria, fungi, and insects. Gall wasps have evolved to “trick” the plant into forming this growth which they then use for food and shelter as they transform from a larva to an adult.

The wasp larvae secrete chemicals that mimic growth hormones in a particular plant upon hatching. The chemicals trick the oak into growing a gall on its flowers, acorns, leaves, or stems. The larva is then encapsulated by the gall as it grows, waiting patiently inside until its metamorphosis is complete.

Above: Feron parmula, commonly known as the disc gall wasp

Many of these plant galls have elaborate, colorful features that are truly stunning.

Above: the spined-turban gall wasp, Cynips douglasii

Gall-forming wasps are only parasitic toward plants -- they do not parasitize other animals. The larvae feed on the nutritive tissues of their plant galls, but the adult wasps do not feed at all.

Above: plant galls produced by two different species of gall wasp

These wasps also have a peculiar reproductive cycle:

Many species have alternating generations, meaning all of the adults emerging from galls during one time of the year are female-only, while the adults emerging in a different season have both males and females. Most species have females that can reproduce using parthenogenesis when they emerge by themselves. This means that their eggs are essentially clones of themselves. What’s more, some species appear not to have any males at all.

Above: the huge, fuzzy plant galls of Striatoandricus furnessae and Druon pattoni

Scientists have named and described roughly 1400 species of gall wasp, and that's likely just a fraction of the number of species that actually exist, as gall-forming organisms are widely understudied.

Above: close-up of a gall wasp larva nestled in its plant gall

Once the larva transforms into a fully-developed wasp, it finally emerges from its gall.

Above: adult gall wasps

Sources & More Info:

Forest Watch: Gall Wasps

Gallformers: What the Heck is a Gall?

Southwick Country Park Nature Reserve: Ecosystem Engineers

Insect Systematics and Diversity: Comparative Anatomy of Venom Glands Suggests a Role of Maternal Secretions in Gall Induction by Cynipid Wasps

Entomology Today: Gall-Inducing Wasps Have Enlarged Venom Glands, Study Finds

The British Plant Gall Society: Plant Galls

As the year comes to a close I wish to inundate you all with some of the coolest, prettiest or strangest wasp photos uploaded to iNat this year, inspired by @cathartidae's wauce blasts

Gonatopus and liopterid

Gasteruption and Cameronella

Eumenine and Smicromorpha doddi

Ammophila wrightii and Stilbula

Pelecinus polyturator and Chrysis viridula

Tracheliodes curvitarsis and Oxyscelio

Orasema and Apoica pallens

Scelionids and Feron kingi

Neotriadomerus and Phlebopenes

Euplectromorpha variegata and chalcids

Antron douglasii and Stylaclista

Synergus and Obenbergerella

Elasmosoma and Polistes dominula

Odontophotopsis melicausa and Stizus texanus

Stypiura and Radumeris tasmaniensis

although they're a fairly generic if slightly spikier brown Andricus orb later in life, Andricus quercustozae galls start out as swollen green buds that quickly turn into these pleasant little cartoon suns. they also attract lots of parasitoids for bonus critter sightings, but you need to be careful when photographing those up close - not because they're easily scared, but because the galls are real icky sticky at this stage

Euderus set, or the "crypt keeper wasp" is a small Eulophid parasitoid of the gall wasp Bassettia pallida.

The female Euderus set will search for the galls or "crypts" induced by the gall wasp Bassettia pallida, but possibly also Andricus quercuspetiolicola and others. The female E. set will then oviposit in the chamber of the gall. When the E. set larva hatches, it will burrow into the host wasp. It then manipulates the host to speed up its development, metamorphoses into an adult, and chews its way up to the surface months earlier than normal. When the host wasp does this, the burrow isn't wide enough for it to emerge from the stem, and its head becomes stuck. The parasitoid then consumes the host and chews through the host's head to emerge as an adult. The larva of E. set overwinters in the gall, eating the host, and emerges the following spring. The mechanism used to manipulate the host is unknown.

This female apparently got overly enthusiastic and took things one step further by wearing her host's head as a costume. Happy Halloween!

[PHOTOS TAKEN: APRIL 13TH, 2026 | Image IDs: two photos showing the cross section of an "oak apple" gall, with a green outside and fibrous white inside, the core at the center being hard and yellow. The last two show the core cut open to expose the beige larva inside /End IDs.]

Disclaimer!: I would not recommend doing this to oak apples, as neither the oak apple galls nor the wasps that produce them are dangerous to the oak tree, and doing this to an oak apple like this will kill the wasp inside. The only reason why I myself cut this gall open is because 1. The gall had already fallen off of the tree, so it wasn't going to be getting any more nutrients from it, and 2. I wasn't actually initially certain what it was (though I did know it was a gall).

This is a kind of oak apple! It's a gall produced by gall wasps of the family Cynipidae, the larva injects chemicals into a leaf of an oak tree that create this round ball of fibrous plant material, the larva living in the center of this ball and sapping nutrients from the leaf!

Another teeny wasp, hooray!

[ID: digital scientific illustration with white text that reads "Blueberry Stem Gall Wasp, Hemadas nubilipennis. The drawings are of a round shiny black wasp with yellow legs and rosy, lumpy gall growing out of a blueberry stem. end ID]

These tiny wasps (2-3 mm!!!) lay multiple eggs per gall at the tip of blueberry stems. This can cause them to stop growing, which blueberry farmers don't like. But they are so cute.