A spider orchid is the common name for Brassia. This genus holds about 35 species closely related to Oncidium orchids. Brassia grows naturally from Mexico through Bolivia and into the West Indies.
Its long, narrow sepals splay out like spider legs, a shape that lures spider hunting wasps. Growers also call this genus orchid brassia, or simply brassia orchids, depending on the region. Each spike can carry a dozen or more of the spidery blooms.
The plants form compressed, flattened pseudobulbs topped with a pair of leathery leaves. Brassia is an epiphyte in the wild, meaning it grows on tree bark rather than in soil. Some species also grow as lithophytes, rooted directly on rock.
That wild background explains why Brassia wants an airy, fast draining mix rather than dense potting soil. Mounting on cork or a slab is also an option for growers with high humidity. A mounted plant just needs more frequent watering than a potted one.
Where Spider Orchids Fit Among Orchid Types
Brassia belongs to the Oncidium alliance, a large group that also includes Miltonia orchid and Oncidium itself. Members of this alliance share similar pseudobulbs. They also share broadly similar culture needs.
That family resemblance is why Brassia care advice often overlaps with Oncidium care advice. If you are still learning the major groups, our overview of types of orchids can help. It shows where Brassia sits among them.
Common names can be confusing across genera and regions. Our guide to orchid names explains how to read a plant tag correctly. That habit saves money and disappointment at nurseries.
Two Other Plants Share the Spider Orchid Name
The name spider orchid also belongs to two unrelated plants. In Australia, Caladenia is the true spider orchid, a ground dwelling genus native to Australia and New Zealand. In Europe, Ophrys sphegodes carries the same nickname, and bees pollinate it instead of wasps.
The rarest of the Australian Caladenia group is the ballerina orchid, known from a single salt lake.
Popular Brassia Orchids and Hybrids
Brassia verrucosa is the most common spider orchid in cultivation. It gets its species name from small greenish warts near the base of the lip. Growers value it for a light, peppery scent that carries across a room.
Brassia gireoudiana comes from Costa Rica and Panama and produces larger, brighter yellow flowers marked with red brown spots. Brassia Rex is a hybrid of those two species. It produces some of the largest flowers in the entire Oncidium alliance.
Brassidium hybrids cross Brassia with Oncidium, adding color range and often a more compact growth habit. These crosses keep the spidery shape but bloom in shades pure Brassia does not offer. A brassia rex orchid can open flowers 10 in (25 cm) across on a mature, well grown plant.
| Type | Typical flower size | Scent |
|---|---|---|
| Brassia verrucosa | Up to 6 in (15 cm) | Light, peppery |
| Brassia gireoudiana | Up to 8 in (20 cm) | Sweet and noticeable |
| Brassia Rex | Up to 10 in (25 cm) | Mild and sweet |
| Brassidium hybrids | Usually smaller, varies | Often light or absent |
How Spider Hunting Wasps Pollinate Brassia
Brassia flowers did not evolve their shape by accident. The long sepals and petals resemble a resting spider. That shape triggers an attack response in certain wasps that normally hunt spiders as food for their larvae.
The wasp stings the lip the way it would sting real prey. In doing so, it picks up pollen from the flower. It then carries that pollen on to the next flower it mistakes for a spider.
This strategy is a form of aggressive mimicry rather than a reward for the wasp. The flower offers no nectar and no real prey inside it. The wasp gets nothing for its trouble except a wasted attack.
Researchers studying Central American orchids have documented this behavior across several Brassia species. The mimicry only has to be convincing at a glance. A hunting wasp reacts fast, and that instinct is exactly what the flower exploits.
How to Grow a Spider Orchid Plant
Brassia wants brighter light than many houseplant orchids, closer to what a Cattleya needs. Give it bright, indirect light or a few hours of gentle morning sun. Leaves that stay grass green without any red blush usually mean the light is too low.
This is one point where generic orchid advice misleads growers. Guides that treat every orchid like a low light Phalaenopsis leave Brassia stuck with healthy leaves and no spikes. If your plant has never bloomed, check light levels before you change anything else.
Intermediate temperatures suit Brassia best. Aim for days around 70 to 80 F (21 to 27 C) and nights near 60 F (16 C). Water when the mix is almost dry, then soak it thoroughly.
In an active growing season that often means watering roughly once a week in bark. Humidity around 40 to 60 percent works well for most homes. Steady air movement around the roots helps prevent rot between waterings.
Fine to medium bark works well, similar to mixes used for Oncidium orchid care. Good airflow around the roots matters as much as the mix itself. Feed at quarter to half label strength during active growth, tapering off as growth slows.
As a brassia orchid matures, it produces multiple pseudobulbs each growing season. Give it a light rest in winter with slightly less water and cooler nights. This is not the harsh dry rest some Dendrobiums need, just a gentler pace.
Check root color to judge whether watering is on track. Firm green or silvery white roots with green tips mean the plant is well watered. Brown, mushy roots signal overwatering, while shriveled gray roots mean the plant has gone too dry.
Brassia sits in the Oncidium alliance. Growers repotting it can follow much of the same routine used for repotting Oncidium orchids. The best timing rule is to repot after new roots appear, not by the calendar alone.
Bark style mixes generally need replacing every 12 to 24 months as it breaks down. Check how much light orchids need before moving a spider orchid to a brighter spot. A sudden jump can scorch leaves that grew in shade.
Common Reasons a Spider Orchid Will Not Bloom
Low light is the most common cause, and it is usually the first thing to fix. A plant kept far from a window may look healthy for years without ever spiking. Move it closer to a bright window or add a grow light before trying anything else.
Rootbound plants sitting in old, broken down bark are another common cause. If the mix has gone soft and soggy, it is past time to repot. A plant with few healthy roots cannot support a flower spike, no matter how bright the light is.
Unlike Phalaenopsis, Brassia does not need a specific cool night trigger to set a spike. Steady bright light and consistent watering matter more than any single temperature drop. A healthy, actively growing plant will usually spike on its own schedule.
Bloom Season and Scent
Most Brassia orchids bloom from late spring through early autumn, with some variation by species and hybrid. A single spike can open ten to twenty flowers over several weeks. Many varieties carry a light, spicy scent that is strongest in the morning.
Some hybrids repeat bloom more than once a year under strong, consistent light. Older, well established plants tend to send up more spikes per season than young divisions. Patience with a newly repotted plant usually pays off within a year or two.
Why Spider Orchid Flowers Last So Long
Unpollinated Brassia flowers can stay fresh for several weeks, longer than many other Oncidium relatives. Once a wasp actually pollinates a flower, that changes fast. The bloom often discolors and wilts within days once the anther cap is dislodged.
This is why growers who want a long display should avoid hand pollinating a spider orchid for fun. Left alone, the flowers hold their color and shape far longer. That patience is part of what makes spider orchids popular with collectors.
Sources
- American Orchid Society: Brassia, Orchids A to Z. https://www.aos.org/orchids/orchids-a-to-z/letter-b/brassia.aspx
- American Orchid Society: Caladenia, Orchids A to Z. https://www.aos.org/orchids/orchids-a-to-z/letter-c/caladenia.aspx
- orchidspecies.com: Brassia verrucosa species page. https://www.orchidspecies.com/brasverrucosa.htm
Frequently asked questions
Is a spider orchid the same as a Caladenia?
No. Caladenia is an unrelated genus of Australian ground orchids. Brassia, the true spider orchid of cultivation, is a Central and South American epiphyte in the Oncidium alliance.
How often should I water a spider orchid?
Water when the bark mix is almost dry, then soak it thoroughly. In warm weather that is often about once a week; in cooler months it can stretch to ten days.
Why did my Brassia flower wilt so fast?
Fast wilting usually means the flower got pollinated, often by a wasp visiting an open window or patio plant. Once pollinated, Brassia flowers discolor and collapse within days.
Can I grow a spider orchid indoors?
Yes, as long as it gets bright light. An unobstructed east or south window works well, or a strong grow light. Weak light produces dark green leaves but few flowers.
What is the largest spider orchid flower?
Brassia Rex produces some of the biggest flowers in the group, sometimes reaching 10 in (25 cm) across. It is a hybrid of Brassia gireoudiana and Brassia verrucosa.