Date: 202004
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Takeoff / Launch
ATC / advisory: Tower ZZZ
Aircraft component: Airspeed Indicator
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Other Takeoff
Result: Flight Crew Took Evasive Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: We were conducting a maintenance ferry flight to ZZZ1 to place the aircraft in storage. The aircraft was secured; properly prepared and [the] crew [was] briefed in accordance with SOP for this operation. On takeoff roll; at the required 100 kts. call by the Pilot Monitoring; the airspeed indicators were observed to be in disagreement by the First Officer; the obvious indication was amber Airspeed Disagree messages on both PFDs. The First Officer verbalized 'airspeed disagree' at which time I looked at both indicators; noted the amber messages and observed my indicator to be approximately 15 kts. higher. My hand was still on the throttles and the aircraft was accelerating rapidly due to the light gross weight. I honestly don't remember if the reject was commenced above V1 because of the airspeed differential; however; I elected to reject the takeoff as the safest course of action. I quickly reasoned the situation might progressively get worse airborne and cause more problems; so I kept the aircraft on the ground.I announced 'Reject' and the First Officer made a call to Tower. We cleared the runway; stopped the aircraft on the taxiway and the Rejected Takeoff QRC/QRG were conducted in accordance with FM procedures. Crew had a conversation about the event and felt the aircraft was safe to taxi and informed station maintenance of the occurrence. We were directed to return to our original gate and received ATC clearance to do so. An electronic logbook entry was made; brake cooling charts referenced; and maintenance personnel were briefed. A thorough crew debrief was also conducted. Maintenance conducted an investigation of the pitot tubes and forward electronics compartment. Their suspicions were proved correct when they postulated the event was caused by mud daubers nesting in the pitot tubes. They had indicated we were the 3rd or 4th event that week. Corrective action was taken; and we flew to ZZZ1 uneventfully. I'm assuming our event was enough of a trend to trigger a bulletin from station operations detailing the problem and corrective actions.


Second narrative: At approximately 90 kts. while on initial takeoff from ZZZ I noticed an airspeed difference (between 5 and 10 kts. difference) between CA (Captain) and FO (First Officer) positions. I attempted to verbalize this difference but not sure if my words were correctly processed by the CA. Immediately following my comments I called 100 kts. At almost the very same time we got an error code 'IAS disagree' light. The flying pilot (CA) made the decision to reject the takeoff and correctly applied the procedure. The airplane stopped very quickly as we had a light fuel land and no passengers (ferry flight). We exited the runway and ran the rejected takeoff checklist. ATC offered assistance but we declined and returned to the gate. After shutting down we were informed by maintenance that the FO side pitot system was compromised by some type of insect (suspected mud dauber). Repairs were completed quickly and we departed uneventfully as soon as our paperwork (maintenance ferry document) was complete.


Synopsis: B737 pilot crew reported erratic airspeed indications which resulted in executing an RTO. A mud wasp nest was found in the pitot system.