All About Butterfly Needles

These can be helpful for blood draws and to deliver IV therapies

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A butterfly needle is a device used to draw blood from a vein or deliver intravenous (IV) therapy to a vein. Also called a winged infusion set or scalp vein set, a butterfly needle consists of a very thin hypodermic needle, two flexible "wings," a flexible transparent tubing, and a connector. The connector can be attached to a vacuum tube or collection bag to draw blood or to tubing from an infusion pump or IV bag to deliver fluids or medications. Medications can also be delivered directly to the connector via a syringe.

Butterfly needles offer certain advantages over straight needles. For instance, they allow for more precise placement, particularly in hard-to-access veins. They aren't the best option in every case, however.

Mistaken Identity

At first glance, a butterfly needle resembles a Huber needle, which is also winged. Huber needles, however, are bent at a 90-degree angle so that they can be securely placed in an implanted chemotherapy port.

What Butterfly Needles Are Used For

Phlebotomists regularly use butterfly needles to obtain blood samples for complete blood counts (CBC), cholesterol tests, diabetes monitoring, STD screens, and other blood-based tests. These needles are also commonly used at blood banks for people wanting to donate blood.

Butterfly needles can also be used to deliver intravenous fluids if you are dehydrated and either cannot drink fluids or cannot drink enough to compensate for fluid loss. They are also useful for delivering medications (such as pain medications) straight into a vein or gradually infusing IV therapies (such as chemotherapy or antibiotics) intravenously.

Though butterfly needles can be left in a vein for five to seven days if properly secured, they are more commonly used for short-term infusions.

Regular or ongoing infusions typically accessed through a larger vein via a central line or peripherally inserted central catheter (PICC) line.

butterfly needles
Verywell / Gary Ferster 


While all butterfly needles are similarly designed, there are variations. Butterfly needles are measured in gauges and typically range in size from 18-gauge to 27-gauge. The higher the gauge, the smaller the needle.

By way of illustration, a 27-gauge needle is the size commonly used for insulin injections. Smaller gauge needles are used if an injectable fluid is thick or if blood is being collected for transfusion. Most butterfly needles are no more than three-quarters of an inch (19 millimeters).

The IV equipment or collection container is attached to tubing that's connected to the needle, rather than the needle. This is helpful, as there is less chance of injury if either is yanked or dropped.

Tubing can range in size from 8 inches to 15 inches (20 to 35 centimeters). Shorter tubes are used for blood draws. Longer ones are intended for IV applications and may have roller valves to regulate the flow. The tubes may also be colored so that nurses can differentiate which line is which if more than one is used.

Some butterfly needle connectors have built-in "male" ports that can be inserted into vacuum tubes. Other connectors have "female" ports into which syringes or lines can be inserted.

How Butterfly Needles Are Used

During venipuncture (the insertion of a needle into a vein), a phlebotomist or nurse will hold the butterfly needle by its wings between the thumb and index finger. Because the hypodermic needle is short and the grasp is close to the needle, the butterfly needle can be placed more accurately than a straight needle, which can often roll or wiggle in the fingers.

The short, thin needle is inserted toward a vein at a shallow angle. Once inserted, the venous pressure will force a small amount of blood into the transparent tubing, providing confirmation that the needle is correctly placed. The wings can also serve to stabilize the needle once it is in place, preventing it from rolling or shifting.

Once used (blood is drawn or medication is delivered), the entire unit is thrown away in a sharps disposal container. The puncture wound is then bandaged.


Because of their small size (far smaller than an intravenous catheter) and shallow-angle design, butterfly needles can access superficial veins near the surface of the skin. This not only makes them less painful to use, but allows them to access veins that are small or narrow, such as those in infants or the elderly.

Butterfly needles are ideal for people with small or spastic (rolling) veins and can even be inserted into the tiny veins of the hand, foot, heel, or scalp.

Butterfly needles are ideal for people who are hesitant about needles because they are less threatening.

They are also less likely to cause profuse bleeding, nerve injury, or a vein collapse once the needle is removed.

Newer models have a slide-and-lock sheath that automatically slides over the needle as it is extracted from a vein, preventing needlestick injuries and the reuse of a used needle.

If you have been told that you have small veins and have had challenging blood draws in the past, you might consider requesting the use of a butterfly needle.


With that being said, butterfly needles are not for everyone.

Because of their small needle size, blood collection tends to be slower. This can be problematic at a blood bank if a person is squeamish or in urgent situations where blood is needed fast. In situations like these, the selection of the needle size is key.

Even for a routine blood draw, the wrong needle size can result in blockage and the need for a second draw if a large quantity of blood is needed.

Because a needle is left in the arm rather than a catheter or PICC line for the purpose of an infusion, a butterfly needle can damage a vein if the unit is suddenly yanked. Even if the right size needle is used, the needle can become blocked during treatment if not correctly placed.

As a rule of thumb, butterfly needles should only be used for IV infusions of five hours or less.

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2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Venipuncture Technique. In: Sedation. 6th edition. 2018:308-318. doi:10.1016/b978-0-323-40053-4.00024-x

  2. Ohnishi H, Watanabe M, Watanabe T. Butterfly needles reduce the incidence of nerve injury during phlebotomy. Arch Pathol Lab Med. 2012;136(4):352. doi:10.5858/arpa.2011-0431-LE

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